Angling causes decline of fish in Canada

Authors: Post, R, Sullivan, M, Cox S, Lester N, Walters, C, Parkinson, E, Paul A, Jackson, L, Shuter, B
Journal: Fisheries | www.fisheries.org | vol 27 no 1
Year: 2002
Where: Canada

This study shows the environmental damage caused by anglers in Canada. They have caused a fish population decline similar to that wrought by commercial fishing. Frighteningly, because political and media spotlights are not on anglers, their harm goes largely unnoticed. The scientists in this research found that:

  • In the last 30 to 40 years, British Columbia has seen, despite increased angler activity, a decline in catch rate of over 600%.
  • Over-fishing in Alberta has caused most of the population of walleye to collapse.
  • In Alberta, catch rates for pike were a fraction of what they were in previous years. Pike have suffered a drop in average age, size, and number.
  • Introducing artificially reared fish causes problems for indigenous fish. Native Ontario lake fish now make up less than half of the population. One reason for this is the eating of native juvenile fish by the larger farmed juvenile fish.
The researchers were concerned that the devastating effect that anglers have caused, in Alberta in particular, may show itself in other Canadian waters, as the human population grows.

"We reject the view that recreational and commercial fisheries are inherently different and demonstrate several mechanisms that can lead to the collapse of recreational fisheries."

"Data from four high profile Canadian recreational fisheries show dramatic declines over the last several decades yet these declines have gone largely unnoticed by fishery scientists, managers, and the public."

"Empirical evidence demonstrates that the predatory behavior of anglers reduces angling quality to levels proportional to distance from population centers. In addition, the behavior of many fish species and the anglers who pursue them, the common management responses to depleted populations, and the ecological responses of disrupted food webs all lead to potential instability in this predator-prey interaction."

ANGLERS DO NOT SELF-REGULATE

"We conclude that recreational fisheries are not necessarily self-regulating."

"The rainbow trout fishery in south-central British Columbia includes approximately 800 trout populations."

"Two populations for which time series are available show that over the last 3-4 decades, substantial increases in total angler effort are coupled with >6-fold reductions in catch rates."

"In Alberta, 21 of 27 walleye populations for which we have data have collapsed because of overfishing."

"Pike populations in Alberta also show strong evidence of over-exploitation leading to collapse; catch rates in the 1990s were only 15% of what they were two decades earlier in 9 pike populations for which we have data."

"Associated reductions in average age, size, number of age-classes in the catch, and failed year-classes all indicate severe overfishing of Alberta pike populations."

"The state of Alberta’s fisheries may be a precursor of what to expect in other jurisdictions as human populations continue to grow and the pressure on fish populations increase."

FOREIGN ANGLERS ADD DESTRUCTION OF FISH POPULATION

"Non-Canadian anglers spent 5.3 million angler-days taking advantage of the perceived unlimited recreational fishing opportunities in Canada."

PREVIOUS POPULATION NUMBERS NOT REMEMBERED

"Declines in populations of long-lived species can be slow, and poor intergenerational memory may lead to declining angler expectations as fish populations decline (coined the "shifting baseline" syndrome by Pauly 1995)."

STOCKING OF NON-NATIVE FISH

"Indeed, the development of the huge hatchery infrastructure in North America in the second half of the last century may itself be credible evidence of the decline of native stocks (Pearse 1988; Hilborn 1992) and also one reason for the apparent invisibility of collapses. We stock a diversity of native and non-native species in waters containing native species despite a large literature on the negative ecological and genetic impacts of these stocking programs (Hilborn 1992)."

HATCHERY FISH REPLACE WILD FISH

"Ontario lake trout are prized recreational fish, yet 60% of formerly viable natural lake trout populations in south eastern Ontario are now maintained partially or exclusively by hatchery propagation (Evans and Wilcox 1991)."

"Stocking on top of depleted wild stocks of lake trout leads to the loss of wild stocks because: (1) the number of artificially produced recruits can easily exceed the number of natural recruits at low natural stock densities, particularly in small lakes, (2) high angling exploitation rates differentially reduces the reproductive potential of the wild stocks, and (3) juvenile hatchery-produced lake trout will cannibalize the smaller-bodied naturally produced juveniles (Evans and Wilcox 1991)."

"Stocking is capable of maintaining exploitation rates well above that which is sustainable by wild stocks, thereby compounding the angling effort imposed on natural stocks. From the standpoint of maintaining natural gene pools, stocking depleted populations is a management response that also acts in a depensatory manner and can hasten the collapse of native stocks."

"The large-bodied freshwater fish species that are the primary targets of many recreational fisheries are successful, in part, due to "cultivation effects," where they crop down forage species that are competitors and/or predators on the juveniles of their own species (Walters and Kitchell 2001)."

"We have evidence from food webs in which walleye populations have been reduced in abundance by exploitation that there has been a predatory release on small-bodied fishes (of the family Cyprinidae) and that these small-bodied fishes both eat and compete with larval and juvenile walleye."

LARGER FISH TAKEN AND SO POPULATION SUFFERS

"Since fisheries tend to reduce the abundance of the larger and more fecund individuals in a population, total population fecundity declines more quickly than numerical abundance. As a consequence of this decline in population fecundity, there is a substantially higher potential for predation by small-bodied fishes on eggs or juveniles of the targeted species."

RECREATIONAL FISHING FOLLOWING
THE DECLINE CAUSED BY COMMERCIAL FISHING

"What is the prognosis for Canada’s recreational fisheries? We argue that if the collapses that we observe in some high profile recreational fisheries are real and general, and remain largely invisible, that many recreational fisheries are headed in the same direction as are the world’s commercial fisheries."
Evans, D. O., and C. C. Wilcox. 1991. Loss of exploited, indigenous populations of lake trout, Salvelinus namaycush, by stocking of non-native stocks. Canadian Journal of Fisheries and Aquatic Sciences 48(S1):134-147.
Hilborn, R. 1992. Hatcheries and the future of salmon in the northwest. Fisheries 17(1):5-8.
Pauly, D. 1995. Anecdotes and the shifting baseline syndrome of fisheries. Trends in Ecology and Evolution 10:430.
Pearse, P. 1988. Rising to the challenge. Canadian Wildlife Federation. Vancouver, British Columbia.
Walters, C. J., and J. F. Kitchell. 2001. Cultivation-depensation effects on juvenile survival and recruitment: a serious flaw in the theory of fishing? Canadian Journal of Fisheries and Aquatic Sciences 58:39-50.
Fish Pain