Fisheries Induced Genetic Selection

Fisheries Induced Genetic Selection


ScienceDaily, January 2 2014. The article asserts that
traditional management on a worldwide basis fails to take into account, quote, the
extraordinary ecological importance of large spawners, and the unintended consequences are
lower harvest in terms of fish and smaller fish within the stock. As it happens, fisheries biologists have known for some time that failing to protect — or even targeting — the large fish in a population can have such unintended consequences. In a 1985 study, Jeffery Hard and three others
reported on two stocks of Chinook transplanted to their Alaska hatchery. They reported, “The difference in rates of early maturity observed between two stocks of Chinook
salmon supports previous findings that male age at maturity in this species is strongly heritable. A 1993 study by David Hankin and others reports that is early is in
1904 “Rutter noted that the selective
removal older and larger fish… resulted in an unnatural abundance of
jacks — meaning small early-returning males. In their
own mating experiment with Chinook brood years from 1978, ’79 and ’80, they showed that mating young two year old males with any age females would produce high ratios of jacks. Daniel Heath and three others observed, “A genetic component to precocious sexual maturation has been
demonstrated in many salmonid species such as Atlantic salmon, Rainbow trout,
Arctic charr, and Cohoe salmon. In their own 1993 experiment on Chinooks, they observe, “The ‘specific jack ratio’ of jack-sired fish (Chinook) was 45%, whereas the ‘specific jack ratio’ of non-jack-sired fish was 27%. In other words, jacks produce jacks at 1.7 times the rate of older male Kings pairing with other kings. From the U-W School of Fisheries, 1995, in a study of 108 populations: “Considerable evidence
indicates that size-selective fisheries may have complex and deleterious effects on Pacific salmon populations. As early as 2002, the Alaska Department of Fish and Game was aware of the issue. They showed that from 1986 to 2001, in-river sport fishers harvested disproportionately older Chinooks than were returning. To the question “Is there a decline in the number of large early-run king salmon in the Kenai River?” they answered “Yes.” And “Consistent disproportionate harvest of early-run king salmon in May and early June could likely have long-term biological
impacts. 2004, Ebsen Olsen and six others in Nature with regard to northern cod: “There is growing anxiety about the consequences of fisheries-induced evolution, because such evolution may
ultimately result in lower sustainable yields and reduced stock stability.” 2005. Birkeland and Dayton. They observe that “Older fishes are usually also larger, and fecundity also increases exponentially with size.” “This is important because commercial
fisheries and especially recreational fisheries often target the larger fish.” And later, “Thus reproductive potential of
populations is disproportionately affected when fishermen target large individuals. 2007. “The biological and economic consequences
of fisheries-induced evolution are potentially severe. Such evolution may
also be slow to reverse, or even turn out to be practically
irreversible.” They observe, “…these evolutionary changes [life history traits: size, age-at-maturity] unfold on decadal time scales– much faster than previously thought — and
the resultant needs for mitigating actions have thus become compelling.” 2007. “Decreasing age and size-at-maturity can induce cascading effects on population dynamics…” “Fisheries-induced evolution was found to be not only possible but also likely under realistic rates of exploitation and size selectivity of fisheries.” “Even in the absence of concrete
evidence for fisheries-induced evolution, rapid
evolutionary responses have been considered so likely that they should be
accounted for in management and conservation strategies.” Last year, 2013, a study involving
17 brood years of Chinook. “Positive relationships between body size
with fitness traits and reproductive success have been well
documented in Pacific salmon.” They add, “For example, skewed sex ratios
within a population can reduce the effective number of breeders and impact mate choices.” We’ve known for decades that the
offspring of Jack Chinook salmon, shown here in blue, are mostly
more jacks. Is this relevant to sustaining
world-class “Kenai River Trophy King Salmon” returns? According to this 2013 report from the
Alaska Department of Fish and Game, the average weight of Chinook
harvested in Upper Cook Inlet has dropped from 34 to just 15 pounds
over the last 25 years. Meanwhile, the percentage of fish aged two years or less has climbed to 66 percent from
10. Fish and Game observes that, “…similar to
other Chinook salmon stocks in Cook Inlet, late-run Kenai River Chinook salmon are experiencing a period of lower abundance, with the 2013 being one of the lowest on record.” And, “The Kenai River early-run Chinook salmon return in 2013 was possibly the lowest on record.” Fish and Game again, this
year, “Because the early-run stock is harvested
primarily by recreational fisheries (marine and river) run size is an important consideration because of its effect on catch rates.” “Small runs are expected for the near future. The 2012 total run was the smallest on record representing more than a four-fold decline from peak abundance in 2004.” And, “During the five most recent brood years (2004 through 2008), productivity residuals
have been negative, … equivalent to a 26 percent decline in
productivity.” In another paper this year, about the Kenai River late-run Chinook, Fish and Game observes, bottom line: “In 2013, 22% of the harvest was one-ocean jacks, the highest proportion of
jacks ever observed. Sex composition was predominately males.” In 2013, the harvest was composed of 88% males, the highest proportion ever observed.” Back to this year’s Fisheries Management
Series, Fish and Game notes: “A major in-river sport
fishery occurs here, and anglers can expend in excess of three hundred (300,000) days per year fishing for Kenai River Chinook salmon.” The sport fishery harvests both early and late run Chinook during the year. But not so commercial fishermen. Fish and Game observes, “The early-run Kenai River Chinook salmon run migrates through Cook Inlet in May and June, and therefore, [because they aren’t fishing it, I add] it receives very little commercial exploitation.” And here we come full circle. There is one
Kenai River fishery, an in-river fishery that indisputably, intentionally, and selectively harvests the largest fish
of any return from both the early-run and late-run of the “World Class Kenai River Trophy King salmon.” And for decades the Alaska Department of
Fish and Game has sanctioned this selective harvest on an
ever-shrinking sub-population of the largest, oldest, most fertile Kenai River Chinooks. The evidence is in. This management
approach has contributed, as expected, to the disappearance of
trophy-sized fish, and more jacks siring jacks, returning
increasing numbers of small fish in a systemic decline leading to the bottom.

4 thoughts on “Fisheries Induced Genetic Selection”

  • Dan, we've been telling our biologists of this concern for the last 10 years to deaf ears…  Thankyou for doing this work to call this to the attention of our experts…

  • Thanks for this, Dan.  It's really nice to see the relevant data in one place.  I hope you've sent this video to ADF&G, FRI (UW), KWF, Alaska Governor's Office and all other germane organizations!!  

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