Fishing about and about fishing
IS SELECTIVITY WRONG?
Since the dawn of modern fisheries releasing the smaller and younger fish from nets has been management’s dogma. We’ve been always told to fish only or mainly older, larger fish, and let the younger and smaller fish grow, mature and procreate. The assumption has been that the surviving spawners will produce huge numbers of eggs and larvae, far enough to replenish the population. Scientists and managers were prescribing minimum hook sizes, and minimum mesh sizes for gillnets, trawl codends, and seine bags.
But more recently, fisheries scientists have started question many of those old, almost axiomatic assumptions. For quite a while now, two Icelanders, Dr. Jonas Bjarnason, and Jon Kristjansson have argued against selective fishing. Although from different points of view, both came to the same conclusion that sustained creaming off the larger and more prolific individuals brings about stock impoverishment, which reduction of quotas and even moratoria won’t cure.
Similar voices came also from the direction of ICES, where in its 2003 Newsletter Nr.40, Dr. Mikko Heino of the Bergen Institute of Marine Research wrote in an article: “Does fishing cause genetic evolution in fish stocks?” (quoted in our March 2004 issue in another context) of genetic changes in selectively fished stocks. In another article Mikko Heino and Ulf Dieckmann report that the collapse of 12 important N.Atlantic and N.Sea stocks was preceded by fish maturing at lowered ages and at smaller size.
And, in the April 2004 issue of “Nature”, Norwegian fishery scientists published a study to the same effect. E.L.Olsen and his co-authors after having analyzed some 30 years of data involving the plunge in Atlantic cod populations around southern Labrador and Newfoundland's Grand Banks, also wrote that there was a decline in the ages and sizes at maturity even before the northern cod population had collapsed, and that the cause was selective fishing pressure against those larger individuals that genetically tend to mature later. The resulting genetic change in the northern cod’s population now slows down its recovery, because the smaller and weaker fish can't produce as many and as strong offspring with desirable genetic properties as the older fish could. Early detection of such evolutionary process could serve as an early warning system for trouble ahead.
According to Steve Berkeley a research biologist at the University of California in Santa Cruz, the same phenomenon is particularly striking in long-lived rockfish species. “Something is just not right with how we are disproportionately removing older and larger fish " - he reported to a recent meeting of the American Association for the Advancement of Science (AAAS). "Sorry - we got it a bit wrong all those years ago. We shouldn't be selectively protecting just the young ones, but adding special protection for the biggest fish. Our research shows that you need to maintain older fish in the population, because those are the most successful at reproducing. But normal fishing at what we now think of as safe levels will not maintain old fish in the population," Berkeley said.
Dr. Bjarnason explains that due to selective fishing more and more stocks abound with smaller, slower growing fish with inferior reproductive qualities. A genetic change occurs in fish populations, and subsequent age groups mature sooner, spending most of their energy on sexual products and spawning at the expense of body growth. They're more vulnerable to predation and their natural mortality increases. It’s quite obvious that culling the older breeders that produce more and stronger larvae can cause genetic selection within fish populations. In almost all cases of stock collapse in the North Atlantic these symptoms have been present, but downplayed or even ignored by the official science
These new findings suggest that erroneous fundamental assumptions underlying current fisheries models result in management decisions that threaten the long-term supply of fish and survival of stocks. Current models assume that (1) within a fisheries management unit (stock), all offspring have an equal probability of survival and of productivity potential, (2) local depletions are temporary, and replenishment will come from other areas, and (3) fishing effects are temporary and reversible. Thus, most managed fisheries are dependent only on maintaining a target level of mature “old” adults that had spawned at least once, while declines below this target are remedied by short-term restrictions on total catch.
So, now when the science is saying that the prevailing approach is inadequate, what can be done? The existence of contemporary evolution and its effects, which can hardly be disputed, requires changes in fisheries management thinking that implies among other things revision of the approach to selective fishing through mesh and hook sizes regulation, as well as timely reducing excessive fishing pressure as soon as distinct genetic changes appear, rather than after populations begin to decline.
In view of all those new and not-so-new findings and the managerial inertia, we must ask whether there’re workable alternatives to the present selective methodology. Admittedly, this traditional management means reduced fishing pressure in terms of number of fish caught. To avoid removal of mainly large individuals from the stock and its consequent degeneration, we must allow catching also those fish that today are considered undersized and also enable survival of sufficient numbers of larger fish. This has to be compensated by other, and hopefully wiser management steps, which should be tailored to each fishery, separately.
Management by quotas wouldn’t be effective, for the quotas would now include also smaller and cheaper fish, which only would amplify discards and high-grading. The new strategy, therefore, would tend towards input-control means that might include access limitations, area and seasonal closures, days-at-sea allocation, gear-size limitations (for example, length of gillnets and longlines, trawlnets circumference, etc), obligatory weekends in harbour, vessel displacement and engine power, and more.
Potent interests would’ve to be dragged kicking backwards out of their preferred quota systems, a task tough but essential if we don’t want to have minnow size cod and haddock all over.