Annual Exploitation Rate Research Articles

Evaluating Exploitation of White Crappie and Black Crappie in Three Southeast Kansas Reservoirs

White Crappie (Pomoxis annularis) and Black Crappie (P. nigromaculatus) were studied in three southeast Kansas reservoirs to assess exploitation and determine if current regulations were conducive for sustainable populations. Trap nets were used to sample crappie in Elk City Reservoir, Big Hill Reservoir, and Parsons City Lake. Crappie measuring 210 mm and greater received Floy FD-94 tags that served as entries for rewards to encourage tag reporting. Harvest and angler demographic information were collected when tags were reported. Postcard surveys and motion-sensed cameras were used in conjunction to estimate angler effort and reporting rate on Parsons City Lake. Annual exploitation rates (i.e., percent of fish harvested) determined by tag returns and corrected for nonreporting and tag loss were 28.3%, 21.8%, and 3.9% on Elk City Reservoir, Big Hill Reservoir, and Parsons City Lake, respectively. Overfishing was not occurring, so current statewide regulations were likely appropriate, and no changes may be necessary.

Population demographics and angler exploitation of Suwannee Bass in two Georgia rivers

AbstractObjectiveSuwannee Bass Micropterus notius are a unique black bass that are endemic to riverine systems in Georgia and Florida, USA. Despite their “near threatened” status by the International Union for Conservation of Nature's Red List, Suwannee Bass are a popular sport fish that can be harvested throughout their range under a single harvest regulation with all black basses (genus Micropterus). However, a single harvest regulation may have disproportion effects on Suwannee Bass because of their rarity, limited distribution, and sex‐specific growth patterns.MethodsBoat electrofishing was used to collect Suwannee Bass and Largemouth Bass M. nigricans from both the Withlacoochee and Ochlockonee rivers to assess population demographics and angler exploitation. Common fisheries assessment metrics were calculated and annual exploitation rate was estimated from high reward (US$100) tags under simulated variability in tag loss and angler reporting rates.ResultWe observed different relative abundance and size structure among river systems. Electrofishing catch per unit effort of Suwannee Bass was higher in the Withlacoochee River (6.89 fish/h) than the Ochlockonee River (2.01 fish/h). Length‐frequency histograms suggested a wide breadth of lengths and presumed ages except for a lack of stock size Suwannee Bass in the Ochlockonee River. Eight percent of monetary reward tags were returned from anglers, yielding an overall exploitation estimate of 3.2%.ConclusionAnnual angler exploitation rates of Suwannee Bass and Largemouth Bass were low (<9.1%) in the Withlacoochee and Ochlockonee rivers of Georgia. Low exploitation coupled with a wide breadth of lengths and ages suggest these populations are currently not at risk of overexploitation.

Participatory stock assessment in West Java contributes to the management of glass eel fisheries in Indonesia

Following the decline of Japanese eel catches and the EU European eel trade ban, other regions, such as Southeast Asia, have become increasingly important sources of juvenile anguillid species for aquaculture. Although appropriate fishery management of tropical eel species is urgently required, data collection by the government or scientific authorities is extremely difficult, because tropical glass eel fisheries are small-scale fisheries conducted in the Global South, where expertise and resources are sometimes limited. To collect data on glass eel fisheries, participatory stock assessments were conducted in West Java, Indonesia, where a Fishery Improvement Project (FIP) and an Aquaculture Improvement Project (AIP) were launched in collaboration with industries, middlemen, fishermen, NGOs, national and local agencies, and scientists. This participatory study successfully collected data on more than 3000 daily fishing practices from approximately 400 fishermen in a single water system in 2019. Even though the assessment was not species-specific, the data collected allowed estimation of the natural mortality rate as being 0.011 day−1. The annual exploitation rate of the glass eel fisheries was estimated as 24.9%, based on a generalised depletion model developed for the data-limited situation where only fishery catch and effort data are available. The data collection scheme for glass eel fisheries was disseminated by local and national agencies to glass eel fishermen in Indonesia and contributed to developing the Eel Conservation National Action Plan.

Per-recruit modelling of pulse fisheries: comment on “Modelling pulse fishery systems in data-limited situations”

Abstract A pulse fishery is one where fishing occurs during a short period each year and is zero for the rest of the year. Grüss et al. proposed a continuous per-recruit model for such fisheries. However, this analysis is based on per-recruit equations that were derived under the assumption that fishing mortality is constant in time and, thus, do not apply to fisheries where F varies, such as a pulse fishery. A correct continuous per-recruit formulation for pulse fisheries is derived. In most cases, the continuous per-recruit model can be closely approximated by a discrete model, where the integrals are replaced by sums. A modification in the Baranov catch equation for pulse fisheries is also derived that can used to compute annual exploitation rates.

Coping with steep exploitation rates in an open access fishery

Fisheries in many developing nations commonly operate in an open access regime, largely due to fundamental factors like poor fisheries institutions and the need to maximize food security and employment. Such factors are evident in Hormozgan, the largest fishing province in Iran, rendering many fish stocks in precarious conditions. The catch of the Indian halibut in Hormozgan has increased sixfold over the past 17 years, along with increasing socioeconomic importance. Yet ever-growing exploitation rates and lack of regulations are threatening both the sustainability of the stock and the livelihoods of fishers that depend on it. In this paper, we examine the status of the Indian halibut using an age-structured model and demonstrate the effectiveness of managing the age selectivity (age at 50% vulnerability to capture (av)) on future biomass and yields under excessive exploitation rates. Our results indicated that the annual exploitation rates had been steadily climbing since 2001, with the stock currently experiences overfishing. Future projections showed that, under intensified exploitation rates (e.g., 0.7 year−1), increasing av from the present 4 years (mean size 39.7 cm) to 5 years (43.3 cm) is expected to maintain biomass at a sustainable level (61% of an unfished level) and enhance yields by 84%. Higher av policies (6 and 7 years) would result in less depletion but forgo substantial yields. This study underscores the potential of size restrictions in sustaining open access fishery resources subjected to steep exploitation rates.

Fishing, environment, and the erosion of a population portfolio

AbstractMany organisms exhibit tremendous fluctuations in population abundance and experience unexpected collapse. Conservationists seeking to minimize region‐wide variability in resources and reduce extinction risk often seek to preserve a metapopulation portfolio of spatially asynchronous subpopulations connected by dispersal. However, portfolio properties are not necessarily static, and the erosion of a portfolio can fundamentally alter the population dynamics and services a species provides. In the Northeast Pacific, a portfolio of spatially asynchronous herring populations has historically provided regional reliability of herring to mobile predators and commercial fishermen as well as local subsistence and ceremonial harvest. Here, we fit a mechanistic time‐series model to herring spawn and catch records from 1950 to 2015 to quantify how population growth, climate, and fishing have contributed to a major shift in the herring portfolio over time. We document the erosion of the herring portfolio and a severe decline in herring population growth. Commercial harvest historically played a key role in herring dynamics, hovering around typical annual exploitation rates (15%) at the archipelago scale, but local harvest rates were much higher when fishing occurred (as high as 65%). Additionally, the Pacific Decadal Oscillation and population growth had equally strong effects on local and regional herring population dynamics. Our results highlight how spatially structured populations can undergo major shifts following disturbance and emphasize how ecological systems do not always rapidly recover and provide services following disturbance. Developing herring management strategies at a finer scale may ensure greater regional resource reliability by recovering previous levels of spatial population asynchrony. However, doing so may require higher implementation and monitoring costs in order to yield higher ecological, social, and economic benefits. Such place‐based solutions that match the spatial scale of governance to the spatial scale of ecological dynamics have the potential to improve future management and conservation in an increasingly dynamic world.

Population status and demographics of Lake Sturgeon in the Bad and White rivers, Wisconsin

Abstract Lake Sturgeon Acipenser fulvescens rehabilitation efforts in Lake Superior are guided by a rehabilitation plan that sets goals and criteria for a self-sustaining population, including a minimum of 1,500 mature adults, roughly equal sex ratio, and annual exploitation rates < 5%. The Bad and White rivers, Wisconsin host a genetically unique Lake Sturgeon population that is utilized by state-licensed recreational anglers and tribal subsistence fishers. Our objectives were to 1) determine if the Bad River population meets rehabilitation plan targets for a self-sustaining population, 2) assess harvest of Lake Sturgeon by recreational anglers and tribal subsistence fishers for compatibility with rehabilitation goals, 3) determine population trajectory from annual spawning runs, and 4) describe population demographics given the unique physical features of Lake Superior. We sampled Lake Sturgeon in the Bad and White rivers with gill nets over a 17-y period (2001 to 2017). The observed sex ratio in spawning runs was 2.2:1 (male : female), but calculated at 1.6:1 for the entire adult population on the basis of abundance estimates. Weight–length relationships converted to a standardized modified form factor indicated lower condition and possibly lower female fecundity compared with other large North American populations. Annual spawning run size estimates over time indicated that the population trajectory was stable to slightly increasing, and during 2016 was 739 and 241 individuals in the Bad and White rivers, respectively. Total population size (including nonspawners) exceeded 1,500 individuals, which met Lake Superior rehabilitation criteria for a self-sustaining population. Estimates of 1,426 males and 882 females were considered conservative because 472 unknown-sex fish could not be accounted for in return time and abundance models. Spawning return times were 2 or 3 y for males and 4 to 6 y for females, longer than many other populations. Exploitation by recreational anglers and tribal subsistence fishers was 1.3% or lower and met the rehabilitation plan target of < 5%, but we recommend exploitation not exceed 3.1% to maintain a self-sustaining population. These findings help gauge rehabilitation progress in Lake Superior and better describe the demographics of a remnant self-sustaining Lake Sturgeon population in Lake Superior.

Population Characteristics of Adult Atlantic Sturgeon Captured by the Commercial Fishery in the Saint John River Estuary, New Brunswick

AbstractThe commercial fishery for Atlantic Sturgeon Acipenser oxyrinchus in the Saint John River, New Brunswick, began in 1880. The early fishery was unregulated, and the adult stock was depleted by 1886 after landings of 712 metric tons. After a 10‐year closure the fishery was reopened in 1897 with management regulations, and landings varied from 6 to 20 metric tons/year until 2010. In 2011 an annual quota of 350 adults was established and landings are now stable at 11.3 ± 1.7 (mean ± SD) metric tons/year. Since 2009, fishers have collected biological statistics from adults taken in the fishery and 14–60% of captured individuals have been marked and released each year. During 2009–2015, annual mean values of total length and dressed weight of landed adults were stable, the male : female sex ratio was 1.2:1.0, and mean age of males and females was 27.2 and 34.0 years, respectively. Estimates of instantaneous total mortality ranged from 0.08 to 0.11, and mean annual survival was 90.9%. Of 1,396 marked adults released, 147 were recaptured in the estuary in subsequent years. Tag returns indicated that the modal spawning periodicity of males was 2 years and that of females was 4 years. Valid, modified Schnabel and Jolly–Seber mean annual population estimates for 2013–2015 were 18,179 and 20,798 adults, respectively. The quota in relation to these estimated adult populations represented annual exploitation rates of 1.9% and 1.7%, which are below F50 and would maintain present stock size. The virgin adult population was determined using 1880–1886 total landings and a mean weight range for adults of 50–30 kg. Estimated range of the 1880 virgin population size was 14,240–23,733 adults. These data suggest that the fishery is sustainable at its current annual yield and that the population is near the carrying capacity of the Saint John River.Received July 12, 2016; accepted November 17, 2016 Published online February 21, 2017

Seasonal Mortality and Movement Patterns of White Bass in a Southeastern U.S. Reservoir

AbstractLittle is known about the fundamental aspects of the life history, ecology, and population dynamics of White Bass Morone chrysops in southern U.S. reservoirs, making management of this species difficult. Recent concerns from the North Carolina Wildlife Resources Commission regarding potential population declines in North Carolina prompted an effort to expand the knowledge base of White Bass in reservoirs. Our study aimed to address mortality (fishing mortality, F, and natural mortality, M) as one potential mechanism related to their population declines and to assess seasonal movement and habitat patterns of reservoir White Bass throughout the year using telemetry. We implanted acoustic transmitters into 50 White Bass in spring 2012 and into 25 White Bass in spring 2013. B. Everett Jordan Reservoir, a relatively shallow and eutrophic reservoir located in the Piedmont region of North Carolina, was separated into four different subbasins that were surveyed each month for tagged fish. Fish were monitored using an array of passive receivers and monthly active tracking surveys. A monthly capture history was used as the input for a multistate capture–recapture model in a Bayesian framework to estimate instantaneous monthly mortality rates. Total annual mortality was 76%. The annual exploitation rate (60%) was greater than the natural mortality rate (15%); however, both F and M exhibited seasonal variation and peaked during spring months in 2012 and 2013. White Bass did not use any specific habitat type but were located relatively far from shore and in deep water during cooler months. The use of subbasins in the system was not equal; other than during the spawning run White Bass concentrated in several areas within the two deepest subbasins of the reservoir. Overall, the high F observed in the spring suggests that adjusting the current liberal harvest limits will help mitigate mortality and aid in the management of reservoir White Bass populations.Received January 21, 2016; accepted May 4, 2016 Published online August 5, 2016

Catch and Exploitation of Shoal Bass in the Flint River, Georgia, USA: Implications for Harvest Restrictions

AbstractShoal Bass Micropterus cataractae are endemic to the Apalachicola River basin (Alabama, Florida, and Georgia) and support popular fisheries, yet little is known about the population dynamics or angler harvest of this species. To estimate the annual exploitation rate (u), 376 Shoal Bass were tagged at 16 sites over a 208‐km stretch of the Flint River, Georgia, during 2008–2011. Mean annual u varied from 0.22 to 0.26, but because of the high movement rates of tagged fish, it was not possible to calculate true u for specific sites along the Flint River. The catch rate of tagged, sedentary Shoal Bass was relatively similar between areas that were accessible by motorboat (0.38) and those accessible only by canoe or kayak (0.32); however, u was 2.5 times higher in the motorboat‐accessible areas (0.22) than in motorboat‐inaccessible areas (0.09). The effects of three length limits (the current minimum length limit [MLL] of 305 mm TL; an MLL of 381 mm TL; and a protected slot limit of 356–432 mm TL) on the Shoal Bass population were explored by using an age‐structured model. Results indicated that growth overfishing did not occur with the current (305‐mm) MLL under the observed range of u, but few fish (≤3%) reached 457 mm, indicating that the population's size structure was likely limited by harvest. The 381‐mm MLL was predicted to cause little decline in yield while (1) decreasing the number of harvested Shoal Bass by 41–42% and (2) increasing the number reaching 457 mm by 37–66%. Performance of the slot limit was similar to that of the 381‐mm MLL in terms of yield and the number of fish reaching 457 mm, but the slot limit was predicted to increase the number of harvested fish by 15–17% relative to the 305‐mm MLL and by almost two‐fold relative to the 381‐mm MLL. The Flint River Shoal Bass fishery is unlikely to achieve a trophy component under the 305‐mm MLL at the observed levels of u. Based on the results of this study, the Georgia Department of Natural Resources adopted a 381‐mm MLL for this reach of the Flint River on September 17, 2014.Received May 27, 2015; accepted January 19, 2016 Published online May 26, 2016

Production rates of walleye and their relationship to exploitation in Escanaba Lake, Wisconsin, 1965–2009

Understanding variability in fish production, biomass, production/biomass (P/B) ratios, and their relationship to exploitation is central to fisheries sustainability. At Escanaba Lake, Wisconsin, USA, data from a compulsory creel census (1965–2009) were combined with survey data on fish populations to test for empirical relationships between annual production and exploitation rates of walleye (Sander vitreus). Empirical estimates of walleye production were relatively high and temporally variable in Escanaba Lake. Annual production, biomass, and P/B ratios ranges were 2.4–11.3 kg·ha−1·year−1, 9.1–49.4 kg·ha−1, and 0.15–0.30 year−1, respectively. Walleye production rates were significantly and positively correlated with adult (i.e., age 3+) walleye density — the core metric used to manage walleye populations in the Ceded Territory of Wisconsin. However, adult walleye density correlated best with ages 4–6 production. Annual exploitation based on the percentage of individuals removed from the population was linearly related to annual exploitation based on the percentage of production removed. On average, 100% of annual production was harvested at ∼20% annual exploitation of individuals; thus, higher sustained exploitation rates would deplete walleye biomass in Escanaba Lake over time. A sustainable annual exploitation rate of 20% annually is lower than the 35% limit reference point currently used for walleye management in the Ceded Territory of Wisconsin. Nevertheless, our estimate is strongly concordant with two recent and independent modeling efforts addressing this same topic. We suggest empirical estimates of fish production are a vastly underutilized tool for better understanding sustainable exploitation rates in walleye populations and, likely, fisheries in general.

Age and growth of invasive lionfish (<I>Pterois</I> spp.) in the Caribbean Sea, with implications for management

Removal efforts designed to avoid or minimize impacts from introduced lionfish, Pterois volitans (Linnaeus, 1758) and Pterois miles (Bennett, 1828), in the western Atlantic Ocean, Caribbean Sea, and Gulf of Mexico will be improved by reliable life history information applicable to the invaded range. For example, length at age has been modeled for lionfish from temperate North Carolina, but parameters characterizing growth are likely to differ in the tropics. Using Pterois spp. from Little Cayman, we validated formation of annual increments and daily rings in sagittal otoliths; documented ages; and estimated parameters for a length-weight relationship, multiple von Bertalanffy growth models, and an asymptotic vulnerability schedule. Formation of annuli was confirmed with marginal increment analysis, and daily ring deposition in juveniles was confirmed using an oxytetracycline hydrochloride marker. Total weight (g) estimated from combined data for both sexes was equal to 0.000003 × total length (mm)3.24. Logistic regression indicated that 50% of lionfish were vulnerable to removal at 129 mm total length. Sagittal otoliths (n = 499) from lionfish collected weekly between January and December 2011 indicated that males were 0-5 yrs old and females were 0-3 yrs old. A maximum likelihood approach to fitting von Bertalanffy equations estimated K and L 8 as 0.42 and 349 mm for the population, 0.38 and 382 mm for males, and 0.57 and 286 mm for females. An age-structured population model indicated that annual exploitation rates of 15%-35% may induce recruitment overfishing, with recovery to 90% of pre-removal biomass occurring 5-20 yrs after removals cease.

Stock assessment of the Spanish mackerel (Scomberomorus commerson) in Saudi waters of the Arabian Gulf with generalized depletion models under data-limited conditions

A multi-annual and multi-fleet version of a generalized depletion model is developed and applied to the Spanish mackerel (Scomberomorus commerson) stock in Saudi waters of the Arabian Gulf under data-limited conditions. The fishing operational data are the official monthly records of estimated catch biomass and exact nominal effort of two artisanal fleets from 1995 to 2012. To transform catch in biomass to catch in numbers, a monthly trend in mean weight is estimated from biological compositional data from 2002, 2013 and used to produce predictions of mean weight for every month between 1995 and 2012. Estimates of natural mortality and initial abundance, thirty six fleet-specific abundance parameters, and six fleet-specific fishing operational parameters, are obtained by maximum likelihood. Thirty six additional timing parameters are fixed by graphical display of catch spikes, a convenient statistic defined here, and by maximum likelihood. The reconstructed history of the stock shows that the catch varies in direct relation to the magnitude of recruitment pulses, while nominal effort has been stable. The annual exploitation rate was estimated at approximately 10%, which implies that fishing is occurring at sustainable levels, although these results are conditional on a well-behaved mean monthly weight in the catch and simplified statistical models.

Growth, mortality and stock assessment of kelee shad, Hilsa kelee (Fam: Clupeidae) in the coastal waters of Pakistan

Growth of kelee shad, Hilsa kelee, in the coastal waters of Pakistan was estimated from the lengthfrequency samples. The von Bertalanffy growth equation was Lt = 23.10 (1 − exp (−0.94(t + 0.18))). Estimated parameters of total mortality (Z), natural mortality (M) and fishing mortality (F) were 2.08 year−1, 1.78 year−1, and 0.30 year−1 respectively. The length-at-first capture was Lc = 10.88 cm. Biomass per recruitment (B/R) and yield per recruitment (Y′/R) were 0.87 and 0.031 respectively. The annual exploitation rate was U = 0.12. The exploitation ratio for maximum yield per recruit Emax = 0.73 and fishing mortality for maximum yield per recruit Fmax = 1.52; biological reference point Fopt = 0.89 year−1 and Flimit = 1.18 year−1. Present estimations showed that the natural mortality was higher than fishing mortality in Hilsa kelee, indicating that the state of the stock is sustainable and the fishery of kelee shad should not be increased beyond current levels in the coastal waters of Pakistan.

Exploring Strategies for Gizzard Shad Removal That Account for Compensatory Density Dependence and Uncertainty

AbstractGizzard shad Dorosoma cepedianum have been the target of removal efforts in eastern North American lakes due to their omnivorous feeding, which may increase nutrient cycling and contribute to high phytoplankton abundance. We used a simulation model to evaluate the efficacy of a gizzard shad removal program at the Harris Chain of Lakes (HCL), Florida, by testing the effects of the exploitation rate, gill‐net mesh size, and harvest interval on the total population biomass and spawning potential ratio (SPR). The analysis accounted for compensatory density dependence of the gizzard shad population and uncertainty in life history parameters. The reductions in gizzard shad biomass and SPR were less than 50% for the two largest mesh sizes (89 and 102 mm) at realistic annual exploitation rates of 0.6–0.8. However, the use of smaller mesh sizes (51 and 64 mm) produced biomass and SPR reductions that exceeded 75% at comparable harvest rates. Current removal efforts at the HCL, which employ a minimum gill‐net mesh size of 102 mm, are unlikely to reduce gizzard shad biomass substantially. However, smaller mesh sizes could result in increased bycatch of economically important black crappies Pomoxis nigromaculatus. Our study sheds light on the importance of using simulation models to forecast the effects of removal efforts on target fish species. The results of such models can be used to inform harvest practices to achieve desired outcomes.Received May 12, 2011; accepted September 12, 2011

Evaluating the Potential Efficacy of Invasive Lionfish (Pterois volitans) Removals

The lionfish, Pterois volitans (Linnaeus) and Pterois miles (Bennett), invasion of the Western Atlantic Ocean, Caribbean Sea and Gulf of Mexico has the potential to alter aquatic communities and represents a legitimate ecological concern. Several local removal programs have been initiated to control this invasion, but it is not known whether removal efforts can substantially reduce lionfish numbers to ameliorate these concerns. We used an age-structured population model to evaluate the potential efficacy of lionfish removal programs and identified critical data gaps for future studies. We used high and low estimates for uncertain parameters including: length at 50% vulnerability to harvest (Lvul), instantaneous natural mortality (M), and the Goodyear compensation ratio (CR). The model predicted an annual exploitation rate between 35 and 65% would be required to cause recruitment overfishing on lionfish populations for our baseline parameter estimates for M and CR (0.5 and 15). Lionfish quickly recovered from high removal rates, reaching 90% of unfished biomass six years after a 50-year simulated removal program. Quantifying lionfish natural mortality and the size-selective vulnerability to harvest are the most important knowledge gaps for future research. We suggest complete eradication of lionfish through fishing is unlikely, and substantial reduction of adult abundance will require a long-term commitment and may be feasible only in small, localized areas where annual exploitation can be intense over multiple consecutive years.

Evaluating relative impacts of recreational fishing harvest and discard mortality on Murray cod ( Maccullochella peelii peelii)

Murray cod Maccullochella peelii peelii support popular recreational fisheries in Australia. Catch and release of Murray cod is common due to regulations and a developing trend of voluntary angler release of harvestable fish, but no previous studies have investigated discard mortality of released fish. We estimated discard mortality by measuring post-angling survival of angler-caught wild Murray cod. Angled fish were monitored for five days after hooking, and overall survival rates of 98% were observed. We explored implications of catch and release as a fishing mortality source by comparing our results to roving creel survey estimates of harvest from six fisheries. We applied the maximum likelihood mortality estimate and upper 95% confidence interval to creel survey estimates of the number of Murray cod that were released in the fishery to estimate the total deaths resulting from catch and release mortality. Estimated ratios of deaths from discard mortality to harvest indicated that high numbers of released fish could contribute as much or more to fishing mortality as harvest in some systems. Future Murray cod research should aim to estimate annual exploitation rates to determine the population-level impacts of fishing mortality, and thus, allow effects of hooking and harvest mortality to be considered in future regulation decisions.

Changes in composition of rockweed (Ascophyllum nodosum) beds due to possible recent increase in sea temperature in Eastern Canada

Ascophyllum nodosum (rockweed) is the main economic resource of the seaweed industry in the Atlantic Provinces of Canada. The annual harvest steadily increased since 1995, reaching a historic peak of 37,000 tonnes in 2007. Due to a high demand for fertilizers and animal feed supplements derived from rockweed, this trend seems likely to continue. The current management plan for the sustainable harvest of the A. nodosum resource is considered conservative. The resource has been managed with a precautionary approach since 1995 to protect the integrity of the habitat. Acadian Seaplants Limited (ASL) has been granted approximately 90% of the government-issued licenses to harvest A. nodosum resources in the Maritimes. The Canadian approach is based on an annual harvest from a given bed and not strip-and-return after several years. Since 1995, ASL has proactively undertaken extensive annual surveys and research on biomass productivity of this renewable resource to establish acceptable annual exploitation rates. Historically, the rockweed beds of southwestern Nova Scotia (NS) have been almost 99% pure A. nodosum, with a minor component of Fucus vesiculosus. However, since 2004, a steady increase in F. vesiculosus, with a peak of 4.6% of the total biomass in 2008, was recorded. This coincided with one of the mildest winters on record for the Maritimes. This increase in temperature seemed to be also responsible for an unusual recruitment of the blue mussel Mytilus edulis in rockweed beds in some areas of southern New Brunswick (NB) in 2006, causing the detachment of up to 30% of the seaweed biomass in some harvesting sectors. Another phenomenon observed in southwestern NS during 2003 and 2004 was extensive ice damage on rockweed beds produced by an early melting of the ice, with losses of up to 90% of the rockweed biomass in some areas.

Modeling the Sustainability of Walleye Populations in Northern Wisconsin Lakes

AbstractPopulation sustainability of walleyes Sander vitreus in the face of angling and spearing fisheries has been a concern of fishery managers in northern Wisconsin since off‐reservation tribal fishing rights were affirmed by federal court decisions. We evaluated sustainability of walleye populations across a range of densities that were subjected to various exploitation rates and allocations of angling and spearing harvest (the fisheries differ in size selectivity). We developed an age‐structured population model for estimating extinction risk and time to extinction for a hypothetical walleye population at a specified exploitation rate, fishery allocation, and initial density. The model was parameterized from data obtained during surveys of walleye populations in northern Wisconsin lakes. Simulations covered a range of annual exploitation rates that included the currently accepted rate of 35% and a range of population densities that are presently included in regression models relating walleye abundance to lake surface area. The risk of extinction began to increase above zero at exploitation rates of 61–65% for an unregulated angling fishery, 85–86% for an angling fishery with a 15‐in minimum length limit, and 77–78% for a spearing fishery. The probability of decline began to increase above zero at exploitation rates of 61–65% for an unregulated angling fishery, 84–85% for an angling fishery with a 15‐in minimum length limit, and 72–77% for a spearing fishery. As the exploitation rate increased, the average adult density decreased and the time to extinction decreased for all initial population densities. We conclude that the current maximum exploitation rate of 35% may be sustainable for all initial population densities but that a controlled field experiment should be used to verify our modeling results before any changes to angling bag limits or spearing quotas are made.

Interactions between poaching and management policy affect marine reserves as conservation tools

To explore the effects of poaching within marine reserve boundaries under three different management policies this analysis uses a simple age-structured reserve model based on yield maximization or reproductive thresholds of Black rockfish ( Sebastes melanops). Departures from the traditional assumptions of full compliance to reserve boundaries alter the conclusions of prior modeling work that demonstrate yield equivalence to no-reserve effort control management and augmented reproductive benefits when small reserves are implemented. By degrading the recruitment subsidization effect to nonreserve areas from protected reserve populations, poaching resulted in negative externalities for compliant fishermen in open areas in terms of yield and degraded the reproductive output and age-structure of the system. All three policies required effort reduction in open areas as a response to poaching in reserves. The strength of the impacts from poaching varied with policy choice and harvest intensity in the reserve, where at the highest level of poaching modeled here (15% annual exploitation rate of the vulnerable reserve population) biological and fishery benefits of implementing reserves were totally negated. Under the assumptions of this model, a policy managing for a reproductive threshold that excludes the reserve population is the precautionary choice if poaching is likely. The results of this exercise emphasize the importance of garnering compliance to reserve boundaries from resource-users for spatial closures to be successful ocean management tools.