How Valuable are our Big Pike?

[AWH]

I was reading over MN's long range management plan for large northern pike when I came upon a very interesting paragraph. It's really an eye opener to just how valuable ONE single pike can be.

The basis for length regulations protecting large northern pike has been research illustrating how large pike are very susceptible to over-harvest. Densities of large northern pike are comparatively low, with fish over 24 inches averaging only about 0.6 individuals per acre compared to densities averaging 9.3 individuals per acre for fish 14 inches and larger (Pierce and Tomcko 2005). The productive capacity of the fish declines rapidly as they get to larger sizes and older ages, yet recreational fishing by all methods tends to select for large, older pike that are the least productive part of the population. Production of fish age 6 and older was estimated to average only 0.1 pounds per acre per year in several north-central Minnesota lakes (Pierce and Tomcko 2003). This is a very low number and shows how large fish can be easily over-exploited. For perspective, it means that removal of only one 10-pound pike uses up the entire production of large pike in a 100-acre lake for a full year. In this example, removal of more than one memorable or trophy size fish would deplete several years’ worth of production.

Thought people would find this interesting. This paragraph happened to be on page 52 of this long range plan that can be found on the DNR website.

Aaron

[sjburnt]

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[fisherking01]

How long does it take a pike to reach 10 pounds?? Seems like a bunch to me. Specific waters which relate to slow growhth factors and low reproduction might encounter a scenario like this, but applying it as a general rule to all waters is rediculous. Am I the only one who observes many large pike in several bodies of water?

I think I need to research more before I can grasp this as factual. Brent

[merkman]

Here is what one guy says.

 Quote:

Northern Pike growth rates (larger view below) vary with lake type and forage base. Lakes with a wide variety of good forage fish will grow Pike faster and larger than lakes with average forage. In stunted lakes (yellow line), Pike grow for a few years, but age and die quickly from the constant struggle to find enough to eat.

All young Pike start out equal. They are opportunistic feeders that will happily feed on most minnows, crustaceans and almost any small game fish that crosses their path. This "puppy chow" type of forage is generally adequate in most lakes, so combined with an abundance of excellent spawning habitat, the stage is set for the production of lots and lots of young Northern Pike. In lakes with average growth rates, a Pike at age 4 is roughly 20 inches and by age 8 reaches the 30-inch range or about 10 pounds.

The privileged Pike that live in waters with lots of food have faster growth rates and the Pike at age 4 could be closer to 24 inches, while the 8-year-old can be upwards of 35 inches. In Minnesota today, any Pike that reaches age ten is a true old timer and could reach 40 inches or about 20 pounds. Today, these larger fish are near the end of the line and very few Pike grow older than ten years of age.

Stunting, the over-abundance of small fish occurs when one of the key elements is out of balance. Most common in our region are lakes that have an abundance of spawning habitat, but too little forage to support the huge number of Pike that these lakes produce. Before a lake can produce large Pike, the smaller fish must first reach a size where they can begin feeding on the larger forage species. The exact forage could vary from lake to lake, but typically Cisco, large Lake Shiners, Suckers or Whitefish come to mind. The point is that these fish need a "super size" meal to reach quality sizes. If their favorite foods are present, they’ll select those. If not, they’ll try to make do with whatever happens to be available. Picture what would happen to your waistline if you’d switch to a strictly T-bone and ice cream diet. If the smaller fish don’t have the chance to grow into the larger categories or if the better foods aren’t available, they get forced into feeding on the smaller forage species, moving constantly in an effort to get enough to eat. It’s enough to keep them alive for a while, but after a few years, even the small Pike begin to die of "old age". This live fast, die fast cycle is literally akin to "eating themselves to death".

Another roadblock in the search for quality Northern Pike is this fishes tendency to be it’s own worst enemy. At times, they’re just too easy to catch! Large Pike feed heavily making them an easy target for hungry anglers who are in turn, all too happy to remove them from their favorite lake. Over time, these larger Pike are over-harvested and the remaining smaller pike compete heavily for food and never attain adequate size required to help move them into the next feeding stage. So even "good lakes" can become over-populated with these stunted Pike. In the end, all too many folks go away with the impression that Pike fishing is just a waste of time. It’s a never-ending downward spiral and unfortunately, a lot of the trouble is our own fault.

You see, in most lakes, Pike are seated firmly at the top of the food chain, so it’s only us (anglers) who have ever removed these larger fish. Because of their aggressive feeding habits, the very presence of these larger Pike could have helped to remove smaller fish from the system. In turn, that would help reduce competition for food and increase the likelihood of more Pike reaching desirable size.

From a fisherman’s point of view, what needs to happen is that more anglers need to value and keep smaller fish for eating. At the same time, we (anglers) need to recognize the importance of returning medium size Pike to our lakes.

- Jeff Sundin

[merkman]

It almost seems the DNR should be stocking ciscos and suckers not Northerns.

[fisherking01]

merkman, thanks for the read. This makes sense and is explained well. I tend to fish very productive waters with extreme rates of growth. My findings are that these pike are consistent with the high growth rate tables. I fish waters that are susceptible to winterkills and growth rates can therefore be compared to known relative ages. Still, I beleive lakes should be managed individually. Brent

[fishcast]

Thanks for posting the articles. I don't quite understand the first article very thouroughly I'll have to look into that more or maybe someone could help explain it better. But I personally couldn't agree more with the second.

I think the main points in the second article are talking about the how the balance of the size structure of the Northern Pike is extremely sensitive in a number of bodies of water compared to other species.

However, I also currently believe this theory is true for a number of fish from sunfish to bass and walleyes up to Northern Pike and more. The reasoning for this is from some minimal personal experience and reading. When you think about it, the most abundant sizes for each species in a water would almost always be the smaller fish, and therefore the ones that put the most strain and competition with the food available in that specific water. Therefore when larger fish are harvested (in this case the 24" plust pike) it to a certain extent, I believe, leaves kind of a resistance to the growth of larger fish in the future. Or, in some cases possibly, the lack of harvest of smaller fish could also cause a similiar "out of balance" affect.

Also, I also wonder when certain species get out of balance (like the lakes with loads of stunted pike or bluegill or even bass or walleye for that matter) how it affects the other fish in the lake?

Just some personal opinion from someone who is definately not by any means an expert on this stuff, just real interested in it. Would like to hear others opinions too.

Also I personally don't think most statewide regs would be the best approach in most cases, and water by water would be best. However, the 24-36" slot for pike, I personally think this one could be a very worthwhile thing to be looking into.

By the way, "How Valuable are Our Big Pike," I say very much, and unfortunately I also feel that for most people they are very undervalued and underated compared to other fish.

[merkman]

 Originally Posted By: fisherking01

merkman, thanks for the read. This makes sense and is explained well. I tend to fish very productive waters with extreme rates of growth. My findings are that these pike are consistent with the high growth rate tables. I fish waters that are susceptible to winterkills and growth rates can therefore be compared to known relative ages. Still, I believe lakes should be managed individually. Brent

I think this is a very good read along with the long range plan.

I think it is very interesting to see in the long range plan that angling takes more than double the fish than does spearing

 Quote:

Creel surveys have shown that spearers harvest northern pike at a rate similar to summer and winter anglers who are specifically fishing for pike, but because there are fewer spearers, spearing harvests have clearly accounted for fewer fish than angling. -Page 43

They go on to say:

 Quote:

Fish length and age data from creel surveys show that spearing harvests contain greater proportions of larger-sized and older fish than angling harvests -Page 43

I read this as a larger proportion of the fish taken by spearing were larger sized, but fewer numbers of larger fish than angling.

 Quote:

(Figure 7) (Pierce and Cook 2000)

Shows that angling (winter and summer) takes twice the number of fish than spearing does.

This is what is very interesting to me from the long range plan.

 Quote:

Where good natural habitat for northern pike exists, natural reproduction is usually not a limiting factor. -Page 43

 Quote:

In fact, a common phenomenon in many small central and northern Minnesota lakes is large numbers of small, stunted northern pike. From a fisheries management viewpoint, these populations are difficult to alter because they arise from some combination of over-harvest of large fish, a lack of appropriate-sized prey fishes, and habitat characteristics that fail to promote good growth. -Page 43

I also agree that lakes should be managed individually because there is no silver bullet.

1) over-harvest of large fish

2) a lack of appropriate-sized prey fishes

3) habitat characteristics that fail to promote good growth.

The DNR has a very hard job in managing these resources.

I do think that all fishermen/fisherwomen have a the task of being responsible in taking the larger fish. This is only one piece of the puzzle though.

The great thing about spearers being responsible in taking big fish is that have the advantage of "look and release" for the bigger fish which leads to a 0% mortality rate vs the 4.5% rate quoted in the long range plan.

 Quote:

Mortality of pike that are caught and released is relatively low, especially if the fish are not deeply hooked. A review of literature on hooking mortality (Tomcko 1997) found an average of 4.5% hooking mortality among six studies (mortality from j-shaped pike hooks, which are more lethal, was excluded). -page 43

As far as points 2 and 3 go:

I question when there are too many small northerns in the lakes, why does the DNR dump more northerns into the lake? It seems to me that when they do this they are increasing the competition for food of the smaller fish thus not letting them get big enough to eat bigger fish and get bigger.

I am not sure they have tried this but it seems to me that if they let natural reproduction take care of the fish breeding and instead concentrate on northern pike habitat and most of all food for them (ie stock prey fish) They would let the over abundance of the small northerns we have now grow to be big fish.

I say lets force feed all them little fishies and make them all GATORS!!!!

It just makes far more sense to me than killing off all the little ones and having them replaced with more little ones through stocking or natural reproduction.

[Hammer Handle]

I have a hard time grasping the article too. Someone can do a study to show there point of view for anything.

When spearing, we have a choice NOT to harm a large fish in anyway. Angling, you do not. When adding in deep hooked fish (not part of the data) and fish that are caught on hot summer days (I bet 30% do not make it)...the numbers of large fish killed compared to spearers is staggering.

Spearing CAN take large fish. But, so can everyone else. We all have a choice.

[shooter_mcgavin]

 Quote:

Spearing CAN take large fish. But, so can everyone else. We all have a choice.

Sure, we all have a choice. But how many spearers out there let the big gators swim by? Unless the sport has changed a lot since I was younger, not too many.

The way I understand it, the importance of big pike is simple. Big pike will eat smaller pike (carnivorous) and keep the population in check. In turn, the small pike don't destroy the forage base, which allows other species to grow and reproduce (for example walleye). A large population of small pike, due to an absence of larger pike to keep them in check, destroys a fishery.

[Hammer Handle]

How many of the same people that spear big norhterns in the winter catch and release the big ones in the summer? Not many, I think.

Catch and release is getting more popular, but don't fool yourself to think that it is the standard now. People that keep the big ones just don't talk about it. They is still a lot of people out to fish for a meal, not a sport.

This is a tough topic, I know. How many people keep the small crappies and throw the big ones back? How many people shoot the deer with the basket rack and let the massive rack go? Like I said, a tough topic.

[merkman]

 Quote:

The way I understand it, the importance of big pike is simple. Big pike will eat smaller pike (carnivorous) and keep the population in check. In turn, the small pike don't destroy the forage base, which allows other species to grow and reproduce (for example walleye). A large population of small pike, due to an absence of larger pike to keep them in check, destroys a fishery.

This is the argument I don't understand.

I would think that a large northern (primarily females) will produce many more little northerns than they could ever eat.

That is how northern pike have survived evolution and are still around today.

If the little northerns are eating all the food in the lake and being stunted why not increase the amount of appropriately sized food available to them (i.e. stock appropriately sized bait fish) and let them grow to be big northerns? Maybe tighten the regulations on commercial fishing of rough fish? The rough fish (among other things) are what make the northerns big. (suckers, ciscoes, etc)

I just can’t seem to figure out how increasing limits on small northerns and limiting taking of big pike is going to solve the problem. All that I see happening is that the small fish will be taken and the large fish will restock the small fish though natural reproduction adding to the problem.

To put it into a farming analogy

If I had 1000 cattle and they were starving, I certainly would not invest my money in wolves to thin the herd. I would buy more hay.

Why slaughter the smaller northerns that are a couple of years on the way to becoming big northerns and replace them with 0 year olds? I will guarantee you that every big northern was once a small northern.

I may very well be all wet here, and I wish someone could explain it to me.

I still can't get my head around this one.

[shooter_mcgavin]

 Quote:

How many of the same people that spear big norhterns in the winter catch and release the big ones in the summer? Not many, I think.

I agree

My point is that most spear-fishermen seem to target the big ones.

 Quote:

People that keep the big ones just don't talk about it. They is still a lot of people out to fish for a meal, not a sport.

I also fish for a meal sometimes, but that doesn't mean I can't be selective. If I have a boat/trailer and vehicle to pull it, and all the necessary license and fees, then I'm probably not in a position that I'm going to starve if I don't keep that big northern. You can be selective and still be out there for a meal. In fact, its going to be a lot easier to catch the smaller ones, since they are so much more numerous.

 Quote:

How many people keep the small crappies and throw the big ones back?

Here's where most hook-and-line guys are guilty of keeping only the big ones.....good point.

Sorry if I got off topic.....

[AWH]

 Originally Posted By: Hammer Handle

How many of the same people that spear big norhterns in the winter catch and release the big ones in the summer? Not many, I think.

Catch and release is getting more popular, but don't fool yourself to think that it is the standard now. People that keep the big ones just don't talk about it. They is still a lot of people out to fish for a meal, not a sport.

This is a tough topic, I know. How many people keep the small crappies and throw the big ones back? How many people shoot the deer with the basket rack and let the massive rack go? Like I said, a tough topic.

This is very accurate. I will say, however, that overall spearers do harvest larger fish on average than anglers. Unfortunately, it's what gives us spearers a bad rap. I wish I could say that all of us as spearers were more conservation minded. Some certainly are. Others, not so much.

Take a look at the graph on page 43 of the following document.

http://files.dnr.state.mn.us/fisheries/muskie_pike/muskiepike_2020.pdf

This confirms what I have said before - as spearers, we are our own worst enemy. I'm not trying to point the finger at just ourselves as spearers. Because there are certainly anglers that have the same mentality. I just think it would be so much easier to change this mentality amongst ourselves, if for no other reason than the fact that we are so much smaller in numbers. If we were able to turn that trend around, we would have the facts to defend ourselves when people choose to go on the attack. Too often I see people saying that they don't spear the big ones and then the next minute are talking about the 10+ pounders that they took. Like I said, let's change that trend. Let's make it so that the facts support that spearers are the most conservation minded folks that are out there targeting pike.

Aaron

[merkman]

 Originally Posted By: shooter_mcgavin

I agree

My point is that most spear-fishermen seem to target the big ones.

I agree to disagree.

[merkman]

 Originally Posted By: AWH

Take a look at the graph on page 43 of the following document.

http://files.dnr.state.mn.us/fisheries/muskie_pike/muskiepike_2020.pdf

This confirms what I have said before - as spearers, we are our own worst enemy.

That graph is very misleading.

Notice how the summer anglers and winter anglers are separated into 2 groups. It makes everything look close to equal.

Imagine that graph if the summer anglers and winter anglers were combined. That is what the lake sees.

[Scott M]

The long range plan and associated literature cited has some great papers and interesting reading. Of all the fish managed in this state, I would bet that in a poll of area fisheries managers, the most difficult fish to manage for has to be northern pike. They get stunted easily, its hard to find them in large sizes, and as a cool-water fish, it is hard to grow them to large sizes without the right suite of conditions.

Did you know it has only been for about 25 years that the state has stopped winter pike rescue efforts? We used to be so obsessed with pike we didn't want to see them die when a lake winterkilled that we moved them to other locations and dumped them in. Talk about ingredients for stunting!

The reading and papers presented here are good, but be careful what conclusions you draw. You won't find a single fisheries management agency in the state stocking prey species. Pretty tough to make sure those prey species survive, are eaten exclusively by pike, don't introduce a disease, etc. Too many risky situations and if things fail its on the DNR and the license dollars used to fund the stocking.

I think the average angler can see just how important catch and release is for those big fish and what an ecological strain it is to remove a big fish, particularly from a small lake. I can remember my father talking about catching all these fish in the teens weightwise on this small, 100 acre lake. Today it's in full stunted mode. It's a nursery for small pike. Pretty hard to shift out of that state.

Just look at these old photos. Like I mentioned, it took the right suite of conditions to grow big pike like in the past, and with time mother nature could provide those conditions. Today, with how much we've changed the landscape and our bodies of water, it is pretty tough for a huge variety of reasons. The best we can hope to do is try to provide some protection from anglers with protected slots and pray for good forage, the right habitat and population densities, good spawning habitat, etc.

(All photos from Minnesota Historical Society)

[merkman]

That last photo puts it into perspective!!

[shooter_mcgavin]

 Quote:

To put it into a farming analogy

If I had 1000 cattle and they were starving, I certainly would not invest my money in wolves to thin the herd. I would buy more hay.

So you wouldn't harvest any? When you do, are you only going to slaughter the biggest, oldest animals? Eventually you're going to have too many cattle for the area in which they are confined, and you're going to have a trampled mud pit and unhealthy animals.

I read a very well researched post on the subject of the value of big pike quite a while ago. It was posted by screen name RK or something. Unfortunately, the search perameters don't allow me to go back and find a link to it.....

To a certain degree, stocking of baitfish might help. However I don't think it would justify the targeting of the biggest, most important fish.

[AWH]

 Originally Posted By: merkman

 Quote:

The way I understand it, the importance of big pike is simple. Big pike will eat smaller pike (carnivorous) and keep the population in check. In turn, the small pike don't destroy the forage base, which allows other species to grow and reproduce (for example walleye). A large population of small pike, due to an absence of larger pike to keep them in check, destroys a fishery.

This is the argument I don't understand.

I would think that a large northern (primarily females) will produce many more little northerns than they could ever eat.

That is how northern pike have survived evolution and are still around today.

If the little northerns are eating all the food in the lake and being stunted why not increase the amount of appropriately sized food available to them (i.e. stock appropriately sized bait fish) and let them grow to be big northerns? Maybe tighten the regulations on commercial fishing of rough fish? The rough fish (among other things) are what make the northerns big. (suckers, ciscoes, etc)

I just can’t seem to figure out how increasing limits on small northerns and limiting taking of big pike is going to solve the problem. All that I see happening is that the small fish will be taken and the large fish will restock the small fish though natural reproduction adding to the problem.

To put it into a farming analogy

If I had 1000 cattle and they were starving, I certainly would not invest my money in wolves to thin the herd. I would buy more hay.

Why slaughter the smaller northerns that are a couple of years on the way to becoming big northerns and replace them with 0 year olds? I will guarantee you that every big northern was once a small northern.

I may very well be all wet here, and I wish someone could explain it to me.

I still can't get my head around this one.

I wish a biologist would come on here and explain this better, as I agree, it can be confusing on "why" it makes sense to harvest the smaller fish and let the big ones go. Yes, the big fish will spawn and create more small pike. But let's say that a 40" pike eats half a dozen smaller pike during the course of the year. That's half a dozen pike that will NOT spawn themselves. So not only do we now have less young of the year pike, but we also have that many fewer pike feeding on the small bait fish that are so valuable in the lakes.

Using another twist, if I'm out to get meat for the table. And pike are great on the table, better than walleye in my opinion! If I believe that one 36" pike will get me as much meat as three 22" pike, what would be better for the system? I am taking three spawners out of the system instead of one. I am taking three fish that are huge eaters of those bite sized bait that all of our pike, walleyes and bass are after. Or I could take one spawner out of the system that feeds on the larger prey in the system, including some of those smaller pike. For the good of the fishery, it just makes more sense to harvest the smaller fish. They are definitely much more plentiful, which I don't think anyone could argue with.

On the stocking bait question...I have heard this question asked of the DNR folks before and in short, their answer was that it just doesn't make sense when it comes down to it. Very, very costly. If they go this route, then they would have to create more hatcheries for suckers, fatheads, tulibees, etc. And as it works, this would then take away from the number of hatcheries that are used for walleyes and other species that are stocked on a regular basis.

A diverse and well balanced fishery is one that will never need to be replenished with forage. That's where we as users of our lakes need to respect the resource by practicing selective harvest, following limits, etc. Those are things that will help our lakes to remain well balanced. Once that gets out of whack, it's hard to get it back.

Not sure if I'm making any sense at all. Just trying to explain things in a less technical way.

Aaron

[bassNspear]

please keep it civil Thanks

[Hammer Handle]

But, the same goes for fishing as duck hunting and many other sports. The numbers and large fish are down do to over-fishing. I really don't think it is from "taking the big ones". Fish don't have the chance to get big for they are caught and kept.

Yes, big fish are important to a lake...but over-fishing and the destruction of lakeshore (weedbeds) have hurt many lakes (if not all in some way).

And I bet all the big northerns in the last picture were caught illegal and during the depression. My dad tells me storys of going to the lake in the spring with a wheelbarrow and pitchfork and filling it with big northerns for pickling so his family could eat.

Times have changed...and it is MUCH easier to get a fish nowadays (less fish and smaller...but our technolgies are more advanced).

If we ban using electronics for fishing, boats with large motors, reels that allow you to cast a mile, and some other advanced items...the fish population would skyrocket in a few years.

Will I spear and keep a big fish? Yes. Do I let some go without spearing? Yes. Will I catch and release all big fish I angle? No. Did I use to keep all big fish? Yes. Do I keep all big fish now? No.

[bassNspear]

I understand that people think that spearing is all about getting the biggest fish. I believe thats wrong. The reason that i say this is becuase in order to keep a lake from gettin gover populated, fisherman have to take the smaller fish as well.

I myself on the other hand, always are looking to just see alot of fish, yes i do once in a while take a bigger fish, but perfer to take the 24-28 becuase there a better eatting fish.

I was talking with a guy that has been spearing for the last 5 days in a row, he has seen over 20 fish, and has only throw the spear one time. This is the point that i bring up, not everyone is out there to spear every pike they see, but to be able to go out and enjoy the fact that you can go out there and see all types of fish, and be able to enjoy that as well.

[AWH]

 Originally Posted By: merkman

That graph is very misleading.

Notice how the summer anglers and winter anglers are separated into 2 groups. It makes everything look close to equal.

Imagine that graph if the summer anglers and winter anglers were combined. That is what the lake sees.

The graph isn't misleading at all. Obviously, spearers don't take more fish than anglers. The number of us that spear just aren't out there. But this isn't what the graph is showing. What the graph shows is the relative size distribution of the fish that are harvested by each group.

Aaron

[AWH]

 Quote:

I read a very well researched post on the subject of the value of big pike quite a while ago. It was posted by screen name RK or something. Unfortunately, the search perameters don't allow me to go back and find a link to it.....

Not sure if this is what you were thinking of. But there was a good discussion on the matter here.

http://www.fishingminnesota.com/forum/ub...true#Post931850

Aaron

[Tom7227]

This may not be the most popular place for my thoughts, but what the heck.

First of all I want to comment on what I have sensed is a way above average respect for the resource as well as other points of view on FM. I have done a little bit of surfing and come back to this website repeatedly because of the quality of the discussions.

That being said - look at some other sites, or even around this website, and you see an awful lot of folks bragging about the size of the fish they took - by hook or by spear. I'm not sure everyone practices selective harvest. I don't really want to bash someone for taking a large fish - that's legal and anyone has a right to do it. But go to the portion of this site where people are displaying photos of the fish they've taken.

I think part of the issue has to do with the amount activity - fight if you will - that you get angling that you don't get spearing. I don't spear. I've watched a friend do it once. My reaction is thinking about being able to play or fight that fish for 1 - 10 minutes with the risk of losing it vs. the spear -bang, it's dead and you bring it up.

It just doesn't sit right with me. It would be a different thing if it was a subsitence situation, but it's not anymore.

[Bowfin]

Tom7227 - Thank you for your view and keeping it respectful. I grew up fishing an awesome northern pike lake in central Minnesota. I "caught" my share of northerns of all sizes and it was exciting. When I was 14, my grandpa taught me to spear - the first fish I speared was 10 lbs. During my teenage years I speared and caught northerns of all sizes. My largest fish I speared was 14.5. The largest I caught was about the same size. Having done both I would rather spear a northern then catch one - whether it be my love of hunting or being sentimental who knows - the anticipation of a large "gator" drifting in excites me more than watching a bobber or holding a trolling rod.

That being said, the lake I cut my "spearing teeth" on became a trophy northern lake with a regulated slot of 24"-36" several years ago. I was forced to let the big ones go. In my conversations with the local fisheries manager, I was assured that this slot wasn't meant to inhibit spearing and although at the time I very much disagreed with the slot, I continued to spear the lake and abided by the slot limit. I had to become a "conservative spearer" - only spearing small fish to be sure I didn't spear one over 24". To date I haven't made a mistake although have speared a couple 23.5 inch fish. Since the slot was enacted the number of large northern we are catching and seeing has increased. I cannot deny that the slot seems to be working to produce a greater number of larger fish.

One last point - In Minnesota I think it is important and possible to provide a variety of northern pike opportunities. I have come to realize the value of providing for some trophy northern lakes (although it was hard personally because they chose the lake I spear on "not in my backyard mentality"). I also think it is important to leave other lakes open to spearing large fish. It concerns me a bit with talk of expanding slot lakes that someday it would lead to a statewide slot. Everyone who spears should have the opportunity to "go after the big ones" from time to time.

[Muskiefool]

This is a Big study AWH but it's a great depiction of what happens to the fisheries when you only harvest the Big fish, its worth the time to read.

LETTERMaladaptive changes in multiple traits caused by fishing: impediments to population recoveryMatthew R. Walsh1,2*, Stephan B. Munch1, Susumu Chiba1,3 and David O. Conover1

Abstract

Some over harvested fish populations fail to recover even after considerable reductions in fishing pressure. The reasons are unclear but may involve genetic changes in life history traits that are detrimental to population growth when natural environmental factors prevail. We empirically modeled this process by subjecting populations of a harvested marine fish, the Atlantic silverside, to experimental size-biased fishing regimes over five generations and then measured correlated responses across multiple traits. Populations where large fish were selectively harvested (as in most fisheries) displayed substantial declines in fecundity, egg volume, larval size at hatch, larval viability, larval growth rates, food consumption rate and conversion efficiency, vertebral number, and willingness to forage. These genetically based changes in numerous traits generally reduce the capacity for population recovery.

Introduction Go to:

It is unclear why some collapsed fisheries fail to recover even after harvesting has been reduced for more than a decade (Hutchings 2000; Hutchings & Reynolds 2004). By targeting the oldest, largest, and fastest growing individuals in a stock, fisheries generate strong directional selection favouring the survival of younger, smaller, and slower growing phenotypes. Recent studies have shown that single traits such as body size, growth rate (Conover & Munch 2002), or age/size at maturity (Olsen et al. 2004) evolve rapidly in response to intense harvest mortality. Because of genetic correlations, however, selective removal of large fish is likely to also cause indirect changes in numerous other traits (Lande & Arnold 1983). Smaller adult body size, for example, may be correlated with earlier maturation, and reduced egg size (Trippel 1995), fecundity (Bobko & Berkeley 2003), larval growth and viability (Berkeley et al. 2004a,. Such changes may accentuate the negative impacts of harvesting.

We conducted a harvest selection experiment on the Atlantic silverside (Pisces: Atherinidae), Menidia menidia, to assess the potential for genetic correlations to cause indirect changes in a variety of traits. We assayed a suite of physiological, meristic, and behavioural characters that either directly or indirectly contribute to fitness, and consequently influence the rate at which overexploited populations may rebound.

The Atlantic silverside is a harvested marine fish commonly found along the east coast of North America (mean annual landings in New York, from 1996 to 2000, were 20.5 MT). This species possesses characteristics common to many marine fishes including external fertilization, small egg size, high fecundity, spawning en masse, pelagic larvae, and schooling behaviour. Yet the Atlantic silverside has an annual life cycle making it one of the few harvested marine vertebrates for which multi-generation selection experiments are feasible. Six captive populations of M. menidia were subjected to one of the following three harvesting strategies (two replicates per treatment): large-size harvest (largest 90% harvested), random-size harvest (90% of fish harvested randomly), and small-size harvest (smallest 90% harvested). After four generations of selection, the yield (biomass) from large-size harvested populations decreased twofold compared with that of small-size harvested stocks wherein yield had increased (Conover & Munch 2002). Changes in yield occurred because large-size harvested fish evolved a slower growth rate and smaller size at harvest and vice-versa for small-size harvested populations. Using fish from the fifth generation of this experiment, here we demonstrate that harvesting the largest individuals caused substantial declines in egg size, larval size at hatching, rates of larval growth and viability, food consumption rates and growth efficiencies, willingness to forage under threat of predation, fecundity, and vertebral number.

Methods Go to:

Harvest experiment protocol

To ensure adequate genetic variation in the founder populations, c. 700 wild adult M. menidia in spawning condition were collected from Great South Bay, NY, USA on 5 May 1998. Fish were transported to the Flax Pond Marine Laboratory, Old Field, NY, USA and divided evenly among two 1800-L tanks supplied with filtered natural seawater. Between 100 000 and 200 000 eggs from these two spawning groups were collected and pooled over a 2-day period. Each generation was reared under identical environmental and density conditions using previously published protocols (Conover & Present 1990). Food was provided ad libitum to allow genetic differences in growth to be fully expressed. In each generation, the six experimental populations were reared in two 'phases' consisting of groups of progeny from each treatment spawned separately over consecutive intervals each spanning 10–20 days of egg collection. The phases represented duplicates of each line that were reared in separate seawater systems as a pre-cautionary measure in case of system failure or disease (neither occurred). Embryos were initially reared at 21 °C. Because M. menidia has temperature-dependent sex determination (Conover & Kynard 1981), larvae between 15 and 90 days old were reared at 15 °C to ensure a balanced sex ratio. Larval density was 175 per 19 L container. At 90 days, 550 juveniles from each phase and population were transferred to 700 L cylindrical tanks. Temperatures were then raised to 27 °C gradually over a 2-week period. When the average age of fish in each phase was 190 days, total lengths of all fish in that phase were individually recorded and sorted by size. The 90th (small-harvest populations) or 10th (large-harvest populations) percentiles of the size distributions were estimated and the appropriate harvest regime was then applied. In control lines, all individuals were also measured but then assigned randomly to either the harvested group or the spawning stock. The two phases of surviving fish within each population were then combined and photoperiod was altered to induce maturity. About 1.5 months later, eggs were collected from spawning tanks and reared as above, and so on for subsequent generations.

Statistical procedures

For all traits measured, differences between lines were examined using a two or three level-nested analysis of variance or covariance. The treatment effect (small, random, large-harvest), and replication (of lines nested within treatments) were the first two levels. A three-level nested anova was necessary for egg volume and larval size at hatch because the date in which the trait was sampled was incorporated. When size varied, it was included as a covariate in ancova.

Egg volume

Samples of 30 eggs per line were measured individually under a dissection scope. This procedure was performed six times.

Larval size at hatching

Hatch size was evaluated by measuring 30, 1-day-old larvae per population on five separate occasions. Failure to obey homogeneity of variances and normality necessitated the use of a Kruskal–Wallis test.

Larval viability

Three replicates, consisting of 50, 1-day-old larvae per line were stocked in 1-L containers. Larvae were fed ad libitum diets of brine shrimp nauplii and rotifers. After 10 days, the remaining living larvae were counted. This protocol was replicated for two separate dates of egg harvest. The data were arcsine transformed and the main effect mean squares were pooled as a result of a non-significant replication term.

Consumption rate and growth efficiency

Trials were conducted under unlimited and restricted ration conditions. The methodologies closely follow prior work (Present & Conover 1992; Billerbeck et al. 2000). For the unlimited food trial: three replicates of six fish per population were fed measured amounts of brine shrimp nauplii for 10 days at 23 °C. The initial lengths of the fish ranged from 18 to 20 mm. Each replicate was established from separate dates of egg harvest. Initial weights were determined by a previously established length–weight regression that consisted of 30 fish per treatment measured for length, wet weight, and dry weight. Nauplii were added, when necessary, to ensure ad libitum conditions.

After 10 days all fish were anaesthetized, and measured for total length, wet weight, and dry weight. Mean food consumption (mg day 1) was calculated as: (food offered – food retrieved)/(number of fish × number of days). Growth efficiency (%) was estimated as the total increase in dry weight divided by the total dry weight consumption of brine shrimp. For the analysis of the unlimited food trial, mean squares were pooled because of a non-significant replication term.

In the restricted ration trial, all lines were given an equal, yet limited, ration. Three replicates of six size-matched fish (mean length from each population: 18 mm) were fed brine shrimp nauplii at a ration of 50% wet fish weight. The remainder of the procedure is the same as above.

Vertebral number

Radiographs of 100 fish per line were taken using a Hewlett–Packard Faxitron Series 43806 X-ray system (50 kVP, 6 mA, 60 s) (Hewlett-Packard Company, Palo Alto, CA, USA) on Kodak Industrex type M film (Eastman Kodak Company, Rochester, NY, USA). All X-rayed fish were 190 days old and were randomly chosen from the fish that were harvested in each treatment during generation five (mean total length: L = 57.7 mm, R = 71.6, S = 81.7). Differences in vertebral counts were analysed with log-linear models. Treatment, line replication, and vertebral number were the factors in the analysis.

Response to predators

The willingness to forage under the threat of predation was evaluated in fish from the large and small-size populations during generation 6. The time of emergence from an experimental shelter after a simulated predatory attack was evaluated. In each trial, five size-matched silversides (mean length 34.8 mm ± 1.1 SD) were transferred to an experimental tank containing a small shelter. After an overnight acclimation period, all fish were chased with a model predator for 15 min until each individual consistently used the shelter to hide. Following another acclimation period (9 h), trials commenced by chasing the fish into the shelter for 15 min and food was then supplied via clear cylinders (1 m long, diameter 3 cm) placed at two corners of the tank. This procedure was replicated seven times.

Sigmoid curves were fitted to the trajectory of emerged individuals after the last chase in each trial, and the time (T50) that 50% of individuals emerged was estimated. T50 were log-transformed to standardize variances and improve normality, and compared among treatments using a one-way anova.

Swimming performance (Ucrit)

Trials consisted of six fish per treatment ranging from 18 to 22 mm. All protocols are based upon prior work (Billerbeck et al. 2001). Twenty-four hours before each trial, fish were size-matched, isolated, and withheld from food. After transferring fish to the flume, trials began with a 15-min acclimation period at a slow flow speed (5–10 cm s 1). Fish were then raised to their initial flow speed (13.5 cm s 1) and raised one body length (2.25 cm s 1) every 10 min. This stepwise increase occurred until all fish fatigued, defined here as failure to hold position and falling back upon the retaining screen. For each fish the time of failure and size were recorded. Exhaustion times were converted to critical speeds by the equation: Ucrit = V + (T /t × v), where V is the highest speed maintained for a full time interval, v the velocity increment, T the time at failure, and t the time increment (Brett 1964).

Results Go to:

Large-size harvesting caused significantly smaller egg volumes (Fig. 1a) and smaller larval size at hatching (Fig. 1b). In addition, estimates of coheritability between size at day 190, and egg size and size at hatch were both significant when maternal size was added as a covariate, indicating that selection on adult size has resulted in genetic changes in both larval traits irrespective of female size (Munch et al. 2005). Larval growth rates were also 25% lower in comparison with randomly selected controls [ancova: F(2,8) = 5.44, P = 0.032]. Furthermore, the probability of survival of these larvae to an age of 10 days was 61% lower than survival in randomly harvested lines (Fig. 1c).

Harvest selection on adult size caused significant declines in the consumption rates and growth efficiencies of juveniles in the large-size harvested lines. Under unlimited food conditions, the slow-growing, large-size harvested fish displayed significantly lower food consumption (Fig. 1d), and growth efficiency (Fig. 1e) when compared with randomly harvested lines. Additionally, even when all experimental fisheries were fed an equal but limited ration, the large-size harvested lines grew slower because of a 25% decrease in food conversion efficiency (Fig. 1f). Willingness to forage under threat of predation also evolved in response to fishing. When subjected to a simulated predatory attack, large-size harvested fish remained in hiding for a significantly longer period of time before resuming foraging (Fig. 1h).

Large changes in fecundity were observed. During generation 5, the fecundity in the large-size harvested populations was c. 60% less than the random-size harvested fish [eggs produced: large-harvest = 23 125; random-harvest = 64 250; small-harvest = 81 175; F(2,3) = 13.01, P = 0.033]. As fecundity is nearly linear with length (Conover 1985), an approximate relative fecundity was calculated based upon the lengths of adults after selection. The relative fecundity of the large-size harvested fish was 66% (± 13) less than the random lines, while the relative fecundity of the small-size harvested fish was 47% (± 20) greater than the random treatments.

Vertebral number also evolved in response to harvest selection. The large-size harvested populations evolved a significantly lower number of vertebrae [Fig. 1g; G = 61.126; P < 0.001].

Discussion Go to:

Fisheries theory assumes that harvest-induced reductions in population size will lead to increased per capita resources, and thereby increased fitness because of release from intraspecific competition (Grift et al. 2003). Implicit in fisheries theory, however, is the notion that changes in fitness are selectively neutral: no allowance is made for the possibility of evolution in response to harvest selection.

In marked contrast, our results demonstrate that a broad array of ecological functions spanning physiology, development, morphology, behaviour, and life history evolve in response to size-selective harvest. Early life history traits such as egg volume and larval size at hatch strongly influence survival. Given that larval mortality of marine fishes typically exceeds 99.9% (Houde 1987), and that the probability of survival is greatly enhanced by larger egg size (Rijnsdorp & Vingerhoed 1994), larval size at hatch, and faster growth (Pepin & Myers 1991; Pepin 1993; Houde 1997), slight reductions in these larval traits may have considerable consequences for recruitment to the juvenile stage. Decreased feeding rate, food conversion efficiency, and willingness to forage all reduce the per capita rate of energy flow and consequently reduce fitness. Finally, reductions in fecundity that occur as a consequence of smaller size will result in direct reductions in fitness.

Thus, despite the belief that increased food availability will increase productivity, we expect harvest selection to decrease the capacity for population recovery by decreasing traits that convert available energy into population growth. Such observations from wild harvested stocks are now accumulating (Sinclair et al. 2002; Barot et al. 2004).

In our experiment, we measured only a small subset of possible correlated traits. Based upon responses to selection in other taxa (Partridge et al. 1999; Garland et al. 2002; Rogers et al. 2005), it is likely that additional traits have evolved. For these reasons, the cascading effects of correlated responses may be far greater than are apparent from this study alone.

That fishing should cause maladaptive changes seems to defy a key principle of evolution. Should not selection favour genotypes with increased viability? The answer is yes, but under intense size-selective fishing, traits that would normally be favoured under natural conditions (e.g. fast growth, high feeding rates and large size) now reduce fitness. In essence, fishing warps the adaptive landscape by selecting against large size, which reduces the value of many correlated characters that ordinarily enhance fitness in unexploited populations. Hence, when fishing pressure is lessened, the survivors are maladapted for an environment where only natural forces prevail. As a consequence, the capacity for population growth in these remnant fish is greatly reduced.

Another paradoxical result is that the small-size harvested fish displayed apparent increases in fitness compared with the controls (Fig. 1). Why were the wild founders of our captive populations not already displaying maximum fitness? The answer is that excessive growth can be detrimental because of trade-offs with other traits. Very fast growing silversides exhibit decreased swimming performance (Billerbeck et al. 2001; Munch & Conover 2004) and a higher susceptibility to predation (Lankford et al. 2001; Munch & Conover 2003). The founders of our experiment came from an intermediate latitude where selection favours a moderate rate of growth. This experiment demonstrates that small or large-size harvest can shift the balance of selection away from the local optimum.

Our results warn that evolutionary responses to harvesting will generally slow the recovery of over-exploited fisheries. Although some of this trait variation may represent phenotypic as opposed to genotypic correlations with size, declines in egg volume, larval size, and fecundity are important from a fishery management perspective regardless of the mechanism responsible. As long as variation in size has a genetic component, the syndrome of undesirable traits that are associated with small size will continue to adversely affect fisheries until large size becomes re-established in the population. How long that would take is unknown. However, because fishing mortality is typically far greater and more selective than natural mortality, the evolutionary reductions in size and correlated changes demonstrated here are likely to persist for some time, even after fishing is halted. We are currently investigating this by continuing our experimental populations with a reduced harvest regime.

Although precise predictions of the response to harvest selection will require a thorough understanding of the genetic covariance structure, some qualitative information about likely paths of evolution may be obtained from the pattern of local adaptation in the wild. Slow growing silversides from low latitude populations exhibit decreased consumption rates and growth efficiencies (Present & Conover 1992; Billerbeck et al. 2000), lower fecundity (Klahre 1997), and lower vertebral counts (Billerbeck et al. 1997) compared with high latitude conspecifics. Thus, the pattern of trait correlations that emerged in response to harvest selection mimics that observed among populations of silversides from different latitudes and demonstrates that the observed changes in large harvested fish are not likely experimental artefacts. This parallelism of genetic correlations within and among populations is common (Schluter 1996) and may be used to establish baselines for predicting evolutionary responses to harvest selection across stocks.

Commercially valuable species typically live for many years, have overlapping generations, and are harvested in a less precise manner than our experimental fisheries. As a consequence, similar responses in wild fisheries are unlikely to be as rapid. Yet evidence documenting phenotypic change for comparable traits in wild fisheries is accumulating (Rochet 1998). Moreover, selective breeding of economically valuable fish species for the purposes of aquaculture have repeatedly demonstrated that many of same traits measured in this study, including egg size (Gall & Neira 2004), fecundity (Su et al. 2002), consumption rate (Mambrini et al. 2004a), food conversion efficiency (Thodesen et al. 1999), and even feeding behaviour (Mambrini et al. 2004b) are also genetically correlated with size. Thus, we expect similar changes to occur in harvested populations, although at a rate commensurate with the generation time of the species in question and the intensity of selection imposed by the fishery.

Of perhaps greater importance are the reasons why some fish stocks fail to recover and others have proven to be quite resilient to exploitation (Hutchings 2000; Hutchings & Reynolds 2004; Hutchings & Baum 2005). We suggest that recovery time may be determined in part by the period and intensity of exploitation to which a population was historically exposed; prolonged exposure to intense selection would increase the likelihood of harvest-induced evolution and thus increase the time required for populations to recover. For example, Atlantic cod, has been harvested for at least 200 years, experienced genetically based declines in fitness related traits (Olsen et al. 2004), and exhibited a little rebound after considerable reductions in fishing. In contrast, similar species with shorter exploitation histories have rebounded in response to diminished harvesting (Hutchings & Baum 2005). This pattern, however, is merely suggestive, and more work is needed to clarify the disparate roles of harvest selection, life-history, community structure, and environmental forcing on the observed differences in recovery.

Many fitness correlates decreased as a result of harvesting the largest individuals in the population. These correlated responses could be indirect responses to a harvest-induced decline in maternal size or adaptive responses to the new fitness landscape. Regardless of the mechanism, they decrease the intrinsic capacity for the population to rebound under natural conditions. A new Darwinian fisheries paradigm is needed in order to account for such impediments to recovery and to ensure sustainable yields over evolutionary time scales.

Acknowledgements Go to:

We thank D. Reznick, J. Arendt, and three anonymous referees for comments on the manuscript that greatly improved its content; and E. Hillebrand, C. Knakal, and numerous members of the Conover Lab for technical assistance. Supported by grants from the National Sea Grant College Program of NOAA under award number NA86RG0056 to the Research Foundation of Stony Brook University for New York Sea Grant, the National Science Foundation (OCE-0081916), and the Pew Institute for Ocean Science of The Pew Charitable Trusts. SC was additionally supported by the Japanese Society for the Promotion of Science. The views, expressed herein, are those of the authors and do not necessarily reflect the views of these sponsoring organizations.

[Tom7227]

I'm not able to absorb a PhD level treatise at this time. One thing does strike me however - how can some legislator stick his/her nose into something as complex as this and even begin to claim to know what they are talking about. People are very quick to criticize the DNR. However it ain't as simple as some would wish. Don't want to hijack this thread but it sure gives you something to think about.

[Scott M]

 Originally Posted By: Bowfin

Tom7227 - Thank you for your view and keeping it respectful. I grew up fishing an awesome northern pike lake in central Minnesota. I "caught" my share of northerns of all sizes and it was exciting. When I was 14, my grandpa taught me to spear - the first fish I speared was 10 lbs. During my teenage years I speared and caught northerns of all sizes. My largest fish I speared was 14.5. The largest I caught was about the same size. Having done both I would rather spear a northern then catch one - whether it be my love of hunting or being sentimental who knows - the anticipation of a large "gator" drifting in excites me more than watching a bobber or holding a trolling rod.

That being said, the lake I cut my "spearing teeth" on became a trophy northern lake with a regulated slot of 24"-36" several years ago. I was forced to let the big ones go. In my conversations with the local fisheries manager, I was assured that this slot wasn't meant to inhibit spearing and although at the time I very much disagreed with the slot, I continued to spear the lake and abided by the slot limit. I had to become a "conservative spearer" - only spearing small fish to be sure I didn't spear one over 24". To date I haven't made a mistake although have speared a couple 23.5 inch fish. Since the slot was enacted the number of large northern we are catching and seeing has increased. I cannot deny that the slot seems to be working to produce a greater number of larger fish.

One last point - In Minnesota I think it is important and possible to provide a variety of northern pike opportunities. I have come to realize the value of providing for some trophy northern lakes (although it was hard personally because they chose the lake I spear on "not in my backyard mentality"). I also think it is important to leave other lakes open to spearing large fish. It concerns me a bit with talk of expanding slot lakes that someday it would lead to a statewide slot. Everyone who spears should have the opportunity to "go after the big ones" from time to time.

I put a lot of stock into a statement like this. It tells me that someone can make short-term sacrifices for long-term gain, and for that I totally give Bowfin and spearers like him credit. They are still able to spear on lakes with slots, they are just careful about how they do it.

Know that you will never see a statewide slot. The anglers are against it, the spearers are against it, and the management agencies are against it. The slot limits in place on certain lakes are tools from the fisheries management toolbox...they are trying to work on a problem in order to get a desired outcome. They don't always work but they are an experimentation and the only way to even try and get results is to do just that- try. You will never see a statewide slot. Minimum size limits cause lots of stacking (oodles of fish approaching the threshold that are too small to keep) and stunting. Maximum size limits are usually for trophy only lakes. A statewide slot would work great on some lakes, not on others, which is why you would never see it.