Study Questions Wisdom of Harvesting Only the Largest Fish

Discussion in 'All Catfishing' started by Spongiform, Jun 8, 2006.

  1. Spongiform

    Spongiform New Member

    I saw the other thread on this topic tonight and thought I'd add this too it - but in a new thread so it wasn't buried 10 pages under!

    Here's the Study ->

    Fisheries managers frequently set minimum size limits for captured animals, mandating that the smallest--and thus youngest--be freed to allow for full maturation. But findings detailed in the current issue of the journal Science suggest that these regulations may actually be shrinking the average size of wild fish over time. Plucking the largest fish from the gene pool, the authors report, leaves only hereditary information from the smallest fish for the next generation.

    To examine the potential evolutionary effects of selective extraction , David Conover and Stephan Munch of the State University of New York at Stony Brook studied a common marine fish called Menidia menidia. Allowing groups of the fish to grow in separate tanks, the scientists removed and weighed the largest 90 percent of individuals from some tanks, the smallest 90 percent from others, and a random 90 percent assortment from the rest. After the remaining fish matured and spawned, the team repeated the process. Initially, the large fish-harvested tanks produced the highest yields. After four generations of such "fishing," however, the total weight of all the fish extracted from the small fish-harvested tanks, as well as the average weight of each creature, amounted to twice that of the large fish-harvested tanks. Additionally, since the reproductive capability of large fish is much greater than that of small ones, small fish-harvesting resulted in more fertile animals. Juvenile survival rates were about the same for all groups, indicating that evolved changes in growth, not viability, caused these results. The findings suggest that in the real world, taking only the largest fish may in the long run result in a calamitous decrease in yield, and thus income, for the entire industry.
    Fishing is big business for many coastal communities. "In New York State alone, the commercial fishing, recreational fishing, and the seafood industries make a $11.5 billion contribution to the state’s economy and employ over 100,000 people," remarks Jack Mattice of New York Sea Grant, one of the funders of this project. A successful industry is based on a healthy fishery, however. "Our study illustrates how well-intentioned management plans that appear to maximize yield on ecological time scales may have the opposite effect after accounting for evolutionary dynamics," Conover notes. The researchers thus propose both creating no-fish areas to prevent an irreversible loss of important genetic diversity, and setting a maximum size limit in addition to the minimum.

    So it's no myth that taking the big ones consistently has a negative effect on the populations.

    Food for thought :D

  2. JAinSC

    JAinSC Active Member

    South Carolina
    Catfish are the perfect species to illustrate the other side of the problem with only minimum size limits, too. Catfish are great at reproducing: they have good parental care and are just very good at producing more small catfish. Catfish, expecially blues and channels, also live a very long time and take a long time to get big. This isn't a problem if you want a lake or river filled with little fish, but if you like great big trophy size fish, then you have to protect the bigger fish simply so they have time to reach the larger size.

    These are 2 separate issues in fishery management: reproduction overfishing and growth overfishing. Very simply, if you kill fish before they can reproduce, then you won't get more little fish (reproduction overfishing) and if you kill fish befreo they can grow up, then you won't have any big fish (growth overfishing).

    Fortunately, the solution seems pretty simple to me. Since they are good at making babies, it's not usually bad for populations (as a matter of fact it can be good - reducing overpopulations in some situations) to kill quite a few little ones. SO, you put a "slot" limit on them. Let people keep a pretty generous nuber of small to medium fish (depending on the fish and the location), but don't let them kill many big fish. Like, for example, you can keep 20 between 12 and 36 inches, but only one over 36. That way you can still have your fish fry, and take a trophy now and then, and still prevent the gluttonous slaughter of big fish that we have all seen from time to time. (The Santee Cooper guides bragging board pictures of 20 dead fish over 30 pounds make me sick to my stomach. Dumb bas&*^%@ are too stupid to see that they are killing their own "golden goose.")

  3. Mr.T

    Mr.T Active Member

    The guide I fished with on Lake of the Ozarks a month or so ago has a policy I really like and have started to follow in my own fishing.

    Release EVERY blue catfish under 20" or over 22". If you want to keep some for dinner, the 20-22" slot is all he'll keep. And no more than 10 fish per trip, period.

    The reasoning is good:

    Smaller fish haven't started being reproductively active yet, so harvesting them at that size doesn't give them a chance to "give back" before you take them.

    Larger fish *are* the core of the reproductive fish. Take one and you take all the potential offspring that fish could have generated.

    Clearly, this is one guide who understands where his livelihood comes from. He logs each and every catch and gives the information to the Conservation Department, which helps them understand the size distribution a little bit better.
  4. FishMan

    FishMan New Member

    how about keeping only channel cats and flats and let the blue become catch and release. I think I heard that blues don't reproduce when small but channel cats do. Does anybody know if this is correct. If at anytime we get to many blue cats they could have a harvest to control numbers. This would make our rivers trophy fisheries.
  5. barbel

    barbel New Member

    I am not sure that this would be the best approach, personally. For one thing, I love flatheads, and I wouldnt want to see them kept while other cats got a better chance at survival. Second, I heard that channels and blues will reproduce almost the exact same. Assuming it was true though, the slot limit on blue catfish could have a higher minimum and lower maximum so that there was more of a chance for the blues to reproduce.

    As for the slot limit, I think that this would solve a lot of problems, from the dwarfism of greater number of fish, to the decreased density of bigger fish. I think that something like 15" to 25" for channels and blues (unless the above condition was true) and for flatheads, 24" to 34" should be ok (correct me if I am wrong on either of these). It would allow people to eat the fish, and keep fairly good sized ones too, but it's usually not good to eat the bigger fish anyways, as they have had more time to accumulate pollutants in their bloodstream.

    Just my two cents :smile2:

    TIM HAGAN New Member

    Well i do about the same thing in my guide service . I let people take cats around 2 to 3 lbs to eat everything over 5 lbs I ask them to let go and 10 lbs and up must be return after photos. C.P.R will keep fish for the kids and they kids. I here where I fish they are best eaten around 2 to 3 lbs.