Perspectives and Policy Recommendations on the Relevance of the Stock Concept to Fishery Management (original) (raw)
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Mixed stock analysis of Lake Michigan's Lake Whitefish Coregonus clupeaformis commercial fishery
Journal of Great Lakes Research, 2016
Six genetic stocks of lake whitefish have been described in Lake Michigan. Concerns exist about the mixed-stock characteristics of Lake Michigan's lake whitefish commercial fishery. The genetic stock-structure model and microsatellite reference database for lake whitefish spawning aggregates in Lake Michigan provide a framework for addressing some key information gaps. These gaps include determining if a mixedstock fishery exists and what level of exploitation each of the six stocks is experiencing. The objectives of this research were: (1) to determine if differential stock harvest occurs in the total commercial catch, (2) determine if spatial differences in genetic composition are present in the harvest, and (3) determine if seasonal differences are present in the commercial harvest. Mixed-stock analysis was conducted on 18 commercial harvest samples collected from spring 2009 to fall 2010. Results showed considerable variability in composition of genetic composition throughout the lake. The samples consisted of 2 to 4 genetic stocks contributing relatively large proportions. The predominant stocks observed in the samples of harvested fish were the North and Moonlight Bay stock (NMB), Big Bay de Noc stock (BBN), the Northern stock (NOR; Epoufette and Naubinway), and the Northeastern stock (NOE; Grand Traverse Bay and Hog Island). For most samples, significant admixture of stocks was present; however, the majority of the samples showed the dominant harvested stock represented <60% of the total sample. Samples from WFM-08 were the most homogeneous, with 80.3% of the sample comprised of the Southern stock (SOU; Saugatuk, Ludington, Muskegon, MI). Multiple samples from WI-2 and WFM-01 across spring, summer, and fall of both sample years showed seasonal differences within in some years, and between years. Interestingly, vii complaints about the most futile frustrations in life. My friends Weston Wise, Mike Blaalid, Karl Nyberg, and Luke Schultz have had many a good time that will not be forgotten. Last, but certainly not least I would like to thank Pete and Sally Beito and the rest of the Blue Goose Gang for all of the wonderful November days spent deer hunting. viii DEDICATION My father Jeff, brother Marc, and uncles Mike and Kevin, and great-uncle Dave have spent countless days in fields, swamps, and on the water and have spurred my interest in a career in the natural resources. This compilation of work is in dedication to these individuals who have inspired and supported me to pursue my interest in fisheries. ix
The true picture of a lake or reservoir fish stock: A review of needs and progress
Fisheries Research, 2009
The conference 'Fish Stock Assessment Methods for Lakes and Reservoirs: Towards the True Picture of Fish Stock' (FSAMLR) was held in September 2007 in Ceske Budejovice, Czech Republic. A total of 110 participants from 34 countries attended the meeting and 93 lectures were presented. Great advances were reported in fish surveys using hydroacoustics and multimesh gillnet techniques, with nearly 60% of all presentations dealing with these topics. In contrast, the use of other active sampling gear, especially trawling and purse seining, received relatively little attention and still requires substantial further development. Reviews of standardization of fish sampling in the European Union, Russia and North America were also presented and clearly showed the benefits of standardized procedures. A number of contributions emphasized the need to use a combination of several methods for the same habitat. A true picture of the fish stock includes knowledge of the abundance, biomass, number of species, size and age compositions. Obtaining results of assured quality for all important lake and reservoir habitats and time periods still presents a significant challenge, although good progress is being made towards this important objective.
Scientific Reports, 2019
Release of captively-bred individuals into the wild is one of the most popular tools in fisheries, forestry, and wildlife management, and introgression of hatchery-reared animals into wild populations is of global concern. However, research and monitoring of impacts on wild populations are generally lacking, and the benefit of hatcheries for long-term fisheries and conservation goals is unclear. Using spatio-temporal genetic monitoring and a four-dacade time series of catch data, we quantified the effects on the size and genetic diversity of wild populations of one of the world's largest marine stock enhancement programs-the red sea bream (Pagrus major) in Kagoshima Bay, Japan. Our analyses found that the stock enhancement program reduced genetic diversity of the population, but the genetic effect diminished with increased size of the wild population. Increases to the seaweed communities and reduced fishing efforts were the primary factors associated with the wild population recovery; effects of aquaculture were much smaller. Our results represent crucial evidence that hatcheries for enhancement and conservation of populations cannot be successful over the long term unless sufficient efforts are also made to reduce harvest rates and rehabilitate natural habitats. Hatchery release is one of the most popular tools in fisheries, forestry, and wildlife management 1 , and it has become a standard conservation tool for Atlantic and Pacific salmon stocks listed under the Endangered Species Act in the USA and at a risk in Canada 2. Huge numbers (>2.6 × 10 10) of juveniles of 180 marine species are released into the wild every year in more than 20 countries, but in most cases monitoring efforts are insufficient to properly assess program effectiveness 3. Research and monitoring of possible impacts on wild populations are generally lacking 1. Although the ability of artificial propagation to maintain populations in the short term is well documented 3,4 , the benefit of hatcheries for long-term fisheries and conservation objectives remains unclear 4,5. The most serious concern is genetic impacts of hatchery-reared animals on wild populations, which has long been discussed for salmon and marine species 6-10. Modern parentage assignment studies provide evidence that the relative reproductive success (RRS) of hatchery-reared steelhead trout 11 , Chinook and coho salmon 12 and farmed Atlantic salmon 13,14 can be only half or less that of wild fish. Marine aquaculture is rapidly growing in Asia, the Mediterranean, and other areas in the world 3 , and genetic effects of huge escapements from fish farms have become a real concern 15. Introgression of farmed Atlantic salmon into 62 wild Norwegian populations of Atlantic salmon was reported at ~6% on average 15-17 , with varying effects on size and age at maturity 18 and other phenotypic and demographic characteristics 19,20. More recently, genetic impacts of farm escapees have been reported for marine fishes 21-24. A systematic review on marine stock enhancement and sea ranching highlighted evidence for substantial gene flow from hatcheries, reduction in genetic diversity in stocked populations, and changes in population structure and life history traits. However, empirical evidence for fitness reduction in stocked and/or
Fisheries Research
The concept of a stock of fish as a management unit has been around for well over a hundred years, and this has formed the basis for the fisheries science. Methods for delimiting stocks have advanced considerably over recent years, using including genetic, tagging and phenotypic information. In parallel with these developments, concepts in population ecology such as meta-population dynamics and connectivity have advanced. The pragmatic view of stocks has always accepted some mixing during spawning, feeding and or larval drift. Here we consider the mismatch between ecological connectivity of a matrix of populations typically focussed on demographic measurements, and genetic connectivity of populations that focus on genetic exchange detected using modern molecular approaches. We suggest that from an ecological-connectivity perspective populations can delimited as management units if there limited exchange during recruitment or via migration in most years. However from a genetic-connectivity perspective such limited exchange can maintain panmixia. We use case-studies of species endangered by overexploitation and/or habitat degradation to show how current methods of stock delimitation can help in managing populations and in conservation.
Ecosphere, 2015
Habitat degradation and harvest have upset the natural buffering mechanism (i.e., portfolio effects) of many large-scale multi-stock fisheries by reducing spawning stock diversity that is vital for generating population stability and resilience. The application of portfolio theory offers a means to guide management activities by quantifying the importance of multi-stock dynamics and suggesting conservation and restoration strategies to improve naturally occurring portfolio effects. Our application of portfolio theory to Lake Erie Sander vitreus (walleye), a large population that is supported by riverine and open-lake reef spawning stocks, has shown that portfolio effects generated by annual inter-stock larval fish production are currently suboptimal when compared to potential buffering capacity. Reduced production from riverine stocks has resulted in a single open-lake reef stock dominating larval production, and in turn, high inter-annual recruitment variability during recent years. Our analyses have shown (1) a weak average correlation between annual river and reef larval production (q ¼ 0.24), suggesting that a natural buffering capacity exists in the population, and (2) expanded annual production of larvae (potential recruits) from riverine stocks could stabilize the fishery by dampening inter-annual recruitment variation. Ultimately, our results demonstrate how portfolio theory can be used to quantify the importance of spawning stock diversity and guide management on ecologically relevant scales (i.e., spawning stocks) leading to greater stability and resilience of multi-stock populations and fisheries.
Evolutionary Applications, 2009
Age and size at maturation have declined dramatically in many commercial fish stocks over the past few decades -changes that have been widely attributed to fishing pressure. We performed an analysis of such trends across multiple studies, to test for the consistency of life history changes under fishing, and for their association with the intensity of exploitation (fishing mortality rate). We analyzed 143 time series from 37 commercial fish stocks, the majority of which originated from the North Atlantic. Rates of phenotypic change were calculated for two traditional maturation indices (length and age at 50% maturity), as well as for probabilistic maturation reaction norms (PMRNs). We found that all three indices declined in heavily exploited populations, and at a rate that was strongly correlated with the intensity of fishing (for length at 50% maturity and PMRNs). These results support previous assertions that fishing pressure is playing a major role in the life history changes observed in commercial fish stocks. Rates of change were as strong for PMRNs as for age and size at 50% maturity, which is consistent with the hypothesis that fishing-induced phenotypic changes can sometimes have a genetic basis.