Fish species today are small and prolific

Human evolutionary pressure has favored species that have short lifespans, begin to reproduce early, and are small-

The findings detailed in the article below are entirely predictable. By selectively killing (overfishing) the largest fish (and biggest animals) humans unintentionally guide the course of evolution to favor the small, quick reproducers. While human caused, this result wasn’t intended, at least not very often.
Modern Fish Communities Live Fast and Die Young. Science Daily





  1. Jim Avatar

    Interesting article, but not surprising. I fish the midwest alot and it seems that numbers of fish are increasing but size is decreasing. I think alot of the genes of larger fish were removed in the last 100 years before catch and release really took off. If the genes of the “trophies” are gone then you simply can’t get big fish.

  2. Immer Treue Avatar
    Immer Treue


    I know there is still good fishing in the midwest, but as with most wildlife, it’s habitat destruction, and overuse/abuse with uncontrolled removal of the “big” ones. How many fishing locales are now filled with tiny bluegills and whatever else can survive, and nothing natural in the waters to prey upon them. In a way, metaphorical for removing large predators from soany habitats.

    That said, MN has done good work in returning sturgeon to many areas. The Sunday Minneapolis St. Paul Star Tribune ran a cover story on the return of sturgeon to the St. Louis river. In part because of the 1977 Clean Water Act and an ambitious joint plan with Canada, a combination of cleanup and stocking of sturgeon has worked. Don’t know how to post the site on this device, but suffice it to say that female sturgeon, that do not begin to reproduce until~25 years old, are now breeding prolifically. This May, the St. Louis river was teeming with thousands of baby sturgeon.

  3. Larry Zuckerman Avatar

    I know about fish… and I don’t know about this claim. Basically, fish are truly plastic phenotypically, including life history strategies. Put a brook trout in a rich, large river and watch it grow. But put the same genetic material with fins and scales into a small, cold, oligotrophic stream with a very short growing season in Rocky Mountain National Park… and watch them stunt.

    I did my MS thesis on life history strategies in two lakes of white suckers that had the possibility of gene flow between them. In the cold, deep, nutrient poor lake the females got larger than the male white suckers, lived longer and reproduced later than the shallower, richer, warmer lake, where males and females were about the same size and much larger than the females of cold lake. Not only did they reproduce at a younger age, they grew faster and died younger. It is like the old r vs K selected species concepts.

    Female fish have a balancing act between energy expenditures for eggs and larvae vs survival and recruitment rates. So.. a female
    can delay reproduction, have larger and more eggs and achieve a certain recruitment rate from her offspring. Larvae from larger eggs have more nutrients and therefore increased chance of recruitment into population as future breeders. Another equally good strategy, particularly for species that repeat spawning year after year is too reproduce at a younger age and get your genes out faster. Also you might have more chances of reproducing annually than one that grows slowly, waits, and might get eaten by a bear or eagle, before ever reproducing.

    Natural selection has equipped most fishes to deal with a wide range of environmental conditions within the boundaries of the tolerances. So a goldfish might live in a bowl for many years and not get too big and probably never reproduce. The same goldfish or its siblings (cohorts in fish biology jargon)placed in a warm river or pond, might get up to 50 lbs – closer to its genetic potential. Fish pretty much have continuous growth until they die.

    In the case of Lahontan cutthroat, genetically the largest Western cutthroat that reached huge sizes in preColumbian Pyramid Lake, Lake Tahoe and other native haunts, pure fish still exist in a cow-bitten little stream in the Great Basin. Of course, it is a little stream that is hammered by livestock so it is warmer, shallower, less insect production, less dissolved oxygen, and therefore produces smaller fish, that tend to reproduce at a younger age and smaller size and then die younger (more r-selected in their life history strategy). Get rid of the hybrids and introduced fishes in Pyramid Lake and restore its habitats including spawning inlets, and watch these remnant pure cutthroat trout grow!

    Fisheries vs fish biology: fisheries management is sort of like elk management in the Rockies – trophy fish being managed above sustainable levels with great anticipation of harvests by licensed anglers. Pressure by anglers forces state fish and game agencies to manage for trophy or at least larger, catchable fish vs what fits the environment. This is particularly problematic in reservoirs, which are artificial aquatic habitats that age rapidly and which fisheries decline soon after filling. Most reservoir fisheries are not self-sustainable and depend on fishery managers and hatcheries.

    Likewise, high mountain lakes, which were largely fishless (supported native amphibians, aquatic insects, and other freshwater invertebrates), were stocked by fishery managers and are often highly dependent on continuing stocking from hatchery fish. Many of these lakes do not have self-sustaining fish populations. Often if you catch a large cutthroat in one of these lakes and it has been stocked for several years, it it most likely an ex-brood stock fish that was stocked as a “trophy”.

    Anyway, I can believe that anglers could select the largest fish in a population, but artificial genetic selection doesn’t happen that rapidly in most fish species in the wild. Also some species are more susceptible to angling pressure than others: brown trout are notoriously harder to catch with rainbow trout then brook trout then cutthroat trout easier and easier. So… for really catchable species like cutthroat trout, angler pressures or commercial netting can rapidly diminish a local stock, while all the fishing regs in the world will have little effect on brown trout populations.

    Let me know if others want additional info

    1. Elk275 Avatar

      The things we all learn in Dr. Ralph Maughan online class room. Thank you. I have loved to fish since I could walk and the above narrative was very educational.

    2. Mark Gamblin (IDFG) Avatar
      Mark Gamblin (IDFG)

      Adding my thanks and praise also. Your points on fish biology, genetics and fisheries management are all on target and helpful to all who read this story and give it critical thought. Well done.

    3. SEAK Mossback Avatar
      SEAK Mossback

      Very interesting, Larry. I have one similar observation. A few years ago I got a call offering a free trip to Jeju Island, Korea if I would write a paper on a rather sweeping topic “Trends in Abundance and Biological Characteristics of Coho Salmon on the Pacific Rim”. One of the interesting things in looking at size was that average weight of coho salmon caught off southern B.C. and in the Columbia River had been in a steady long-term declining trend since the 1950s which had been commented on by many authors including the eminent W.E. Ricker as early as 1980. All suggested the likely cause was the selective effects of fishing which was quite intense until the mid-1990s. However, by the time I looked at it in 2005, average size had bottomed in 1992-1993 after declining by 60% in the West Coast of Vancouver Island troll fishery (less in the Columbia River) and had fully recovered to around the earliest measured weights in only a decade. While it is true that fishing was greatly curtailed in those areas in the 1990s, the long, steady decline and rapid rebound in size pretty much mirrored the rise and fall in the number of hatchery coho smolts released in the same region. It was more pronounced in stocks in Puget Sound and Georgia Strait than those on the outer coast where fish dispersed more directly into ocean waters, suggesting competition for food with an increasing density of hatchery fish was the likely cause of smaller size, rather than the selective effects of fishing pressure. Coho salmon virtually all (except jacks) spend 1 year in the ocean, so variation in average age is not a factor.

  4. smalltownID Avatar

    No catch and release program for big game. Some research with big game coming out of ISU similar to this. Keep an eye out for it. Interesting stuff.


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Ralph Maughan