Runty Lingcod?

I've wondered about this when I see the pictures of big Lings up in Alaska.  Are we breeding a strain of runty lingcod down here by taking all the big ones?  Check out this article where a biologist bred a strain of runty fish in four or five generations to prove a point about the lack of recovery in the Atlantic cod fishery.  Maybe we need a rotating slot limit or something.


http://www.npr.org/templates/story/story.php?storyId=5434698

Interesting article.  However, it is my belief that we are not breeding runty lingcod but catching them before they grow to larger sizes. 

Jason

I hate half logic......................

Yes, you can create a "line" that will show a selected trait, in nearly any species on this planet, in 3-4 generations.  But calling that "evolution" is a bit of a reach.  It is a family or tribal trait. 

Until you are down to profoundly tiny population this is not significant in the long run because all of the genetic makeup for the trait that wasn't selected for is still there.  When a new pressure is applied to the population, the expression of the formerly "fatal" gene may be selected for and the population will again look different in 3-4 genereations.

So, yeah, slot limits could change that because if the length or weight trait is a part of the population, it will then be differentially selected for.

call it what you want, but if maxed out 23.99" adult ling cods are out there,
they get to stay out there while the 27" end up as dinner.

trait selection is the mechanism for evolution over enough time. time is accelerated for a fast growing and breeding
fish like a lingcod.  or a dog.

I'm not a bio professional, but my own definition of "species" is that members can successfully reproduce.
A toy poodle and great dane might be genetically compatible, but traitwise, they might not be viable.
By that argument trait selection over a few hundred years made a new species.

There is also a biomass argument, you can only have 1 42"  20lb ling cod for 4 24" 5lb ling cod, I'm okay with
a few more but smaller myself.

If the reefs get overrun with 23.99" lingcod, I'm sure they can go with a slot and fix it in the same amount of
it took them to cause the "problem" in the first place.

J

Cool, David Conover (the scientist in the article) is the professor I took fisheries biology with in grad school.

Anyway, evolution is change in traits brought upon by natural selection (or in this case fishing pressure).  Occasionally that change in traits is enough to create a new species, however you don't need a new species formed to have proof of evolution.

The "runts" in this case are not just a population of short fish that we fishermen haven't caught yet, rather they are a population that actually matures at a smaller size and begin reproducing much earlier than the original population.   It is this shift in reproduction is problematic in that smaller fish don't have as much
reproductive output (i.e. number of eggs) than the larger fish.  Because of this, the populations recover much slower.  This is in fact evolution of a reproductive trait, but not necessarily evolution of a new species.
 
Brian

brian, wouldn't there be more of the smaller fish? therefore the total volume of eggs would be the same.
the biomass argument again.

those tiny brook trout and blue gills, there can be a lot of them.

On the other hand, coho salmon will eventually evolve to survive in crappy water.  Win some, lose some. 

A species is really a dynamic thing, and once we've been around long enough to see it happen everywhere, people will accept that and hopefully take a more realistic look at the way the biosphere works with regards to anthropological effects and endagered species ect.  Half of our problem these days is half the country thinks god only gave us yay many species and everywhere you look some mal-adapted thing is on the brink. 

The coho comment is going over my head due to my ignorance on coho, would you care to elaborate? thanks.

J

I don't buy the evolution thing in this case.

I feel that people have just harvested the bigger ones, or can't get to them as they are deeper than regs allow you to fish.

I highly doubt that angling pressure has any evolutionary pressure on the fish other than just pulling out the bigger ones.

A slot limit would help this problem.

MolBasser

First of all the research done for the study mentioned in the article wasn't on fish in the field that are under fishing pressure, rather they were done on silversides in a lab.  Silverides can reproduce several times a year and grow to maturity fairly quickly.  The researchers removed the larger fish from the experiment which selected for fish that can reproduce earlier than normal.  After several generations, the remaining population had a size at maturity that was significantly smaller than the original population.  Even if you stop removing the larger fish, this change in size at maturity persists.  From this, the researchers discuss their research in light of current problems with some fisheries.

Secondly, egg production and body size are not linearly correlated, rather the relationship tends to be exponential.  A 25 lb fish will produce many more eggs than 5 fish that are 5lb.  As an example, I just looked at a figure (2b) in a paper by McIntyre and Hutchings (2003)
http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?_handler_=HandleInitialGet&journal=cjfas&volume=60&calyLang=eng&articleFile=f03-090.pdf
that looked at the size fecundity relationship of Atlantic Cod.
 
Anyway, in that figure (fig 2b) the log of the fecundity (egg count) is plotted against the weight of the female fish and a linear line is fit to the relationship.  In other words, fecundity increases exponentially with weight.   Extrapolating from the graph we find that a 2000 g female produces roughly 270,000 eggs where as a 10000 g female procudes 3.2 million eggs.  In other words a fish 5 times as heavy produces  12 times as many eggs.


Brian

Yeah, I guess I ought to read the paper.....

MolBasser

His postulation that marine protected areas will prevent this is utter bull$#!+ too.  Either fish travel in and out of reserves so quickly that they have no effect, or the fish outside the reserves are selectively bred to be smaller, while the ones inside are not selected one way or another.  The smaller fish from outside breed with the unbiased ones inside and have smaller young.  Either way natural selection still works, though it may be slowed by a marginal amount.

I'd be willing to bet that due to the limitations of his net's length and radius and his 'handedness' - scooping to the left or to the right, there were areas in his tanks (bottoms, corners, sides) that he did not scoop.  De facto MPAs in his experiment that did not prevent him from selectively breeding runty fish.

Slot limits or a screen on the net to reject large fish would do much more to limit harmful evolutionary pressure on the fish than MPAs ever could.  A slot limit would even serve to provide evolutionary pressure to grow faster and larger!

Of course selective breeding and genetic engineering (or restoration in this case) could be used to produce hatchery fish with their 'big fish' genes intact or possibly enhanced to provide a continuous counterbalancing force to the downward pressure in size caused by fishing with only a minimum size limit.

If fishing is to be sustainable indefinitely, folks must come to realize that we cannot just take take take without giving anything back.  Just like we cannot farm without breeding, planting, weeding, watering and fertillizing.  If we take breeding grounds, we should provide alternate means of reproduction.  If there isn't enough foodfish, the harvest of them should be discouraged.  If an undesireable species (squid, gopher rockfish, pinepeds) is stealing eco-share, it's harvest should be encouraged or even subsidized.  And if genetic drift is occurring in a bad direction, measures should be taken to counteract it. 


Regarding the salmon, living in warmer streams with lower flows is applying natural selection to them that will eventually make them more tolerant of those conditions.  Between global warming and the non-negotiable need for water, they will be forced to adapt in the end.  Perhaps they'll eventually spawn at a differnt time, go to sea sooner or become heat and disease resistant, but if they're kept in a marginalized condition eventually they'll find ways to make the best of it.

brian thanks for the note on the many eggs from big fish thing. it's not what I would have intuited,
but I don't doubt it.

I have one more counter,  , for you to re-counter on why the smaller fish might not be so bad.

I wonder what the survivability of the fewer eggs from the smaller fish is? since they are more dispersed,
they could have a better average suvivability than a big pile of eggs from a larger fish?
I guess that's why scientists do experiments.

josh thanks for the coho note. so coho are threatened because we don't have coho hatcheries like we
do for chinook?

btw, I heard coho don't taste very good. is that true? I hear the flesh is mushy?

J,

While it is true that spreading out egg dispersal in time and space does reduce varibility in survivability, we are probably talking about tens of thousands of large fish versus hundreds of thousands of small fish.   So, I don't think the difference would be that great.  Besides, many fish can and do spawn on multiple occasions to even out this risk.   I believe this is true of the Atlantic cod which broadcast spawn, but not true of lingcod which lay their eggs in guarded nests.

While we're on the topic of differential survivability, there has been some research done that suggests that the really large fish not only have more eggs, but that their eggs are of better quality.  The quality in this case is inferred from the diameter and lipid content of eggs from various sized individuals.  No one has been able to determine whether these differences in lipid store and size actually make a difference in long term survivability of the larvae to recruitment into the fishery.

Brian

>josh thanks for the coho note. so coho are threatened because we don't have coho hatcheries like we do for chinook?

Coho are threatened because of an extended period of poor weather conditions coupled with water diversion and habitat degredation.  Hatcheries could dramatically increase their numbers, but 'threatened' is a politically defined term that currently excludes hatchery fish, so they'd still be 'threatened' if you could walk to japan on the backs of hatchery coho.  Some of our chinook are 'threatened' dispite hatcheries. 

With that logic, presumably those folk would allow famined people in africa to die of starvation to use them as poster-children in a campaign against global warming, deforestation/desertification and unsustainable farming techniques instead of providing them food aid.  After all, it's un-natural to give them food and we should instead try to repair their habitat.