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Contributions of a conservation measure that protects the spawning stock to drastic increases in the Gulf of Maine American lobster fishery
Abstract
V-notching, a conservation measure intended for the protection of mature female lobsters, has been hypothesized to have contributed to the dramatic increase in American lobster Homarus americanus landings and stock biomass in the Gulf of Maine. To evaluate the impact of this conservation measure, scenarios examining different v-notching compliance rates and vnotch definitions were simulated using an individual-based lobster simulator with different re cruitment dynamics scenarios. In the model, v-notching with a high compliance rate and a strict de finition of the ‘notch’ increased spawning stock biomass by 33−632%. Without a stock− recruitment relationship, v-notching with high compliance and a strict definition decreased landings by 2%. With a weak or strong stock−recruitment relationship, v-notching with high compliance and a strict definition increased landings by 33−85%. Without a high v-notching compliance rate (i.e. 90 or 100% compliance) or a strict definition of the notch, the lobster stock and fishery would not have experienced such large positive increases in biomass and landings. These results suggest that input controls, such as protecting the spawning stock, can provide significant benefits to both the fish population and fishery. The framework proposed in this study can be extended to evaluate the protection of spawning females in other fisheries.
Supplementary resource (1)
... Management of the GOM American lobster fishery focuses on protecting the spawning stock through a combination of minimum and maximum legal sizes and v-notching, which have been found to have contributed to strong historical stock productivity (ASMFC, 2020; Le Bris et al., 2018;Li, 2018;Mazur et al., 2019). Thus far, only a handful of studies have evaluated the contribution of conservation measures to the productivity of the GOM lobster fishery. ...
... While promising, these results should be interpreted thoughtfully. An artifact of the weak stock-recruitment relationship based on the 1982-2013 time-series is that there is a strong nonlinear positive relationship between SSB and recruitment (Li, 2018;Mazur et al., 2019). Thus, our results may be based on optimistic estimates of recruitment. ...
... Thus, our results may be based on optimistic estimates of recruitment. Despite SSB increasing, if the spawning stock becomes dominated by smaller females, egg quality and quantity could diminish (Hixon et al., 2014;Koopman et al., 2015;Mazur et al., 2019;Ouellet & Plante, 2004). Furthermore, if temperatures enter a range that is physiologically stressful for lobster, as has already led to stock collapse in Southern New England (ASMFC, 2020;Quinn, 2017;Shields, 2013), the positive effects of climate change on SSB and landings may be dampened. ...
Crustaceans, which are highly susceptible to the effects of climate change, are critical for food security worldwide. Yet, management rarely evaluates the performance of alternative regulatory strategies under climate-driven life history change. This limits the development of climate-ready management plans, undermining fisheries sustainability. We compared the performance of alternative minimum legal size (MLS) regulations under shifts in growth and maturity for American lobster in the Gulf of Maine, the most valuable single-species commercial fishery in the United States. Across the life history change scenarios examined, increasing MLS improved status indicators, while decreasing MLS eroded status indicators for spawning stock biomass, legal abundance, landings, and exploitation rate. Our results demonstrate that protecting the lobster stock by increasing MLS improves fishery output, highlighting that conservation and industry goals can be complementary. This study exemplifies the utility of MLS as a conservation measure for crustacean fisheries under climate change.
... They recreated abundance time-series for both regions and showed that protecting large, fecund females was important for fishery resilience and capitalizing on favorable environmental conditions in the GOM. Additionally, Mazur et al. (2019) evaluated the effectiveness of v-notching under different recruitment dynamics and stock-recruitment relationships. Finally, Li (2018) simulated how minimum and maximum legal sizes contribute to lobster landings, abundance, and biomass under different stock-recruitment relationships. ...
... The simulations implemented three climate-driven directional changes to life history identified in the literature and confirmed via the expert survey: decreasing SAM (Haarr et al., 2018;Le Bris et al., 2017;Waller et al., 2019Waller et al., , 2021, decreasing molt increment size and increasing MP (Landers et al., 2002;Waddy et al., 1995). A weak stock-recruitment relationship, as described in Mazur et al. (2019), was used for all scenarios to capture the feedback between spawning stock size and recruitment. In the weak stock-recruitment relationship, recruitment is drawn from a normal distribution with means and standard deviations estimated from the stock assessment output that correspond to five levels of SSB (ASMFC, 2015). ...
... While SSB may increase, lower quality eggs could negatively impact recruitment. However, whether this manifests as a negative impact on the stock will depend on the size structure of the mature female component of the population (Hixon et al., 2014;Mazur et al., 2019). If enough large and highly fecund females are contributing to overall egg production potential negative impacts could be counteracted. ...
... This conservation measure has been found to have positive impacts on lobster fisheries. For example, v-notching has an important role in the Maine lobster fishery; it contributed to the drastic increases in lobster biomass and landings [27]. Additionally, Daniel et al. [28] and Tully [25] found that the v-notch conservation measure increased the reproductive potential of lobster populations off the coasts of Maine and Ireland, respectively. ...
... If compliance continues to decline, the effect of v-notching on future sustainability will change, which may further affect lobster fishers' perception of v-notching. Although the lobster catch has increased partially due to v-notching [27], this increase has created unintended consequences that are challenging the norm such that for some lobster fishers, v-notching is no longer a priority (Fig. 1). Before resource abundance dramatically increased, the cost of v-notching compliance was low and relatively easy to do [46]. ...
Understanding compliance is important for understanding the effectiveness of conservation. This study examines conservation compliance in the American lobster fishery in Maine. In this fishery, an important conservation measure that protects spawning female lobsters, known as v-notching, is considered a norm. This conservation rule is primarily self-enforced, but evidence suggests that its compliance rate may be declining. We analyzed semi-structured and oral history interviews to understand v-notching compliance and lobster fishers' perceptions of v-notching. All lobster fishers interviewed described v-notching as important for the lobster fishery's sustainability, while also reporting that the v-notching practice has been declining in recent years. Conservation compliance changed as the benefits of conservation changed. Because of large lobster catches, lobster fishers have begun to question whether v-notching is as necessary as it was in the past. High catches in recent years also created time constraints on board the vessel that limit the ability to v-notch. Long-term changes in abundance and consequently landings impacted the norm of v-notching. Under new conditions of the lobster resource, v-notching as a norm may be weakened, as there are now conflicting views on the benefits of v-notching. The implications of a reduction in v-notching may be significant for the future sustainability of this fishery given studies that have shown the conservation value of this practice. This study highlights the importance of considering changes in conservation compliance in adaptive management plans due to changes in benefits and costs caused by changing resource conditions.
... Het aantonen van een positieve relatie tussen lokale toename van maatse vrouwtjes en lokale aanwas van jonge kreeft was met deze studie echter moeilijk aan te tonen(Tully, 2001). Resultaten van een modeleringsstudie voor de Amerikaanse kreeft visserij in Maine suggereren dat v-notching, bij een goede handhaving, zelfs bij een zwakke relatie tussen vrouwtjes en aanwas zal leiden tot een grotere biomassa kreeft en daarmee betere visserijmogelijkheden(Mazur et al., 2019). ...
Lobster fishers possess a wealth of experiential knowledge about their fishery, the biology and behaviour of lobster, changes in lobster stocks and catch composition, changes in the ecosystem and interactions between them. Based on five research questions, this study has systematically collected the experiential knowledge of fishers targeting European lobster (Homarus gammarus) in the Dutch Eastern Scheldt (Oosterschelde) through interviews and an annual questionnaire. The aim of the study was to make this
experiential knowledge accessible to fishers, fisheries researchers and managers. The study is part of the so-called LobStAR project, which is funded as part of the Dutch operational programme of the European Fund for Maritime Affairs and Fisheries. The project was carried out jointly by Wageningen Marine Research and the fisheries association OWV.
... This conservation measure was called into question in the 1980s when opponents (state, interstate, and federal) spoke against the practice and tried to abolish it from the fishery despite its well-established history and ground support from harvesters and across the industry (Acheson and Brewer, 2003 ). In recent years, MEDMR and other researchers have paired industry knowledge of this practice with MEDMR lobster programme data (which records the presence and type of v-notch on each female) to quantify the immense long-term benefits this conservation measure has had on the population and the GOM fishery (Le Bris et al., 2018 ;Mazur et al., 2019 ;. Currently, MEDMR has one of the few broadscale monitoring programmes that studies all life stages of the American lobster from planktonic larvae to adults harvested in the fishery. ...
The Maine Department of Marine Resources (MEDMR) is a state agency tasked with developing , conserving , researching , and promoting commercial and recreational marine fisheries across Maine's vast coastline. Close collaborations with industry members in each of the 30 or more fisheries that support Maine's coastal economy are central to MEDMR's efforts to address this suite of tasks. Here we reflect on recent decades of MEDMR's work and demonstrate how MEDMR fisheries research programmes are preparing for an uncertain future through the lens of three broadly applicable climate-driven challenges: (1) a rapidly changing marine ecosystem; (2) recommendations driven by state and federal climate initiatives; and (3) the need to share institutional knowledge with a new generation of marine resource scientists. We do this by highlighting our scientific and co-management approach to coastal Maine fisheries that ha v e prospered, declined, or followed a unique trend over the last 25 + years. We use these examples to illustrate our lessons learned when studying a diverse array of fisheries, highlight the importance of collaborations with academia and the commercial fishing industry, and share our recommendations to marine resource scientists for addressing the climate-driven challenges that motivated this work.
... However, seasonal HSI does not change drastically between low and moderate abundance regimes. This suggests that the lobster boom and initial increase in lobster abundances may be due to other factors beyond just climate-driven habitat, such as a conservation focused management and a decrease in predators (Zhang and Chen, 2007;Zhang et al., 2012;Mazur et al., 2019). The model can, however, hindcast much more reliably to a moderate (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) and high (2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018) abundance regime. ...
Continued warming of oceans has caused global shifts in marine species distributions. This can result in changes in the spatial distribution of landings and have distributional impacts on marine resource-dependent communities. We evaluated the spatial dynamics of American lobster (Homarus americanus) landings in coastal Maine, which supports one of the most valuable U.S. fisheries. We coupled a bioclimate envelope model and a generalized additive model to project spatial dynamics of lobster landings under possible climate scenarios. This coupled model was then used to forecast future lobster habitat suitability based on IPCC RCP climate scenarios and predict distributions of fishery landings from this projected lobster habitat suitability. The historical spatial distribution of fishery landings shows the highest proportional landings in Maine’s Southern (southwest) regions. The current distribution of landings shows higher proportional landings in Downeast (northeast) regions with the highest proportional landings in Midcoast (middle) regions. Our results suggest that while the proportion of landings in each zone will remain stable, changes in habitat suitability in the spring and fall will reduce total landings. Future habitat suitability is projected to decrease in spring but increase in fall in Downeast areas. Downeast landings are projected to decrease in the next 30 years, then increase over the subsequent 80 years, depending on RCP scenarios and abundance regimes. Midcoast landings are projected to decrease while Southcoast landings are expected to stay constant. This study develops an approach to link climate change effects to fishery landings. These findings have long-term implications for sustainable, localized management of the Maine lobster fishery in a changing climate.
... For example, management of the fishery for American lobster Homarus americanus in the Gulf of Maine has included mandatory marking of egg-bearing females by fishers (i.e., by cutting a V-shaped notch in the tail) and restrictions on the retention of marked lobsters that are subsequently recaptured (Lockhart and Estrella 1997;Acheson and Gardner 2011). In addition to serving as protection for female spawning biomass (Mazur et al. 2019), the marking program has provided information on demographics and reproductive dynamics (Walz and Bayer 1988;Daniel et al. 1989). ...
Sensitivity analyses have identified uncertainty regarding sex ratios within commercial landings of Pacific Halibut Hippoglossus stenolepis as an influential source of variance within annual stock assessments for this species in U.S. and Canadian waters. Sex composition of dockside landings cannot be directly observed because all retained fish must be eviscerated at sea, and sex cannot be visually determined in the absence of the gonads. In the current study, a marking program was evaluated in which sex‐specific marks were applied by fishers to their retained catch, the mark was recorded during dockside monitoring, and the accuracy of the recorded sexes was validated using genetic techniques. The chosen marks (two vertical cuts in the dorsal fin for females and a single cut in the operculum of males) were considered by fishers to be easy to apply during at‐sea processing and produced sex‐ratio estimates that were equivalent to genetic results for 65% of sampled landings. However, vessel‐ and region‐specific accuracy was variable. Additional incentives to encourage vessels to participate in the program, continued outreach, or potentially a regulatory requirement to mark fish would be required to produce sufficient data to satisfy stock assessment needs, and ongoing validation would likely need to accompany such a program to ensure consistent and acceptable data quality.
... FVCOM data have been widely used for hindcasting distributions or HSI for many species (Decelles et al. 2015;Torre et al. 2018;Runnebaum et al. 2018;Mazur et al. 2019). ...
The Gulf of Maine northern shrimp (Pandalus borealis) once supported a significant winter fishery for the Gulf of Maine (GOM). Although the shrimp fishery is not comparable to the lobster business, it provided fishermen and many coastal communities jobs and incomes in winters after lobster seasons. However, a moratorium has been put on the shrimp fishery since 2014 due to record low population abundance and perceived recruitment failures. The recruitment failures have been correlated with warming water temperatures over the past decade. The GOM has been recognized as experiencing rapid warming as a result of global climate change. Uncertain impacts of the changing environment on the life cycle and the fishery of northern shrimp could hamper the efforts to rebuild a resilient and sustainable shrimp fishery. Consequently, there is a pressing need to understand the impacts of climate change on the life cycle and population dynamics of the GOM northern shrimp. The objectives of this research project are to 1) develop a cost-effective sampling protocol for building a comprehensive fecundity database including maternal body size, and number and size of eggs; 2) examine the impacts of climate-induced environmental variabilities on egg mortality; 3) develop a complete size-fecundity relationship in order to derive a robust estimate of reproductive potential of the population; 4) illuminate the effect of water temperature on spatial structure for each life stage; and 5) investigate the relationship between environmental variabilities and habitat suitability in northern shrimp spawners’ distribution. The findings reveal that the GOM bottom temperatures might have changed considerably over the past fifty years; however, the correlation between water temperature and parasitic infection eggs was not significant and the changes in reproductive potential might be related to population density rather than bottom temperature. The results also showed that the distributions of mature groups were getting patchier and shifting northward, which were correlated with declined population abundance and warming temperature, respectively. Furthermore, the quality of habitat has declined significantly for mature groups in summer and fall, especially in the 2010s, which could result from warming temperature and subsequently lead to declined spawning stock biomass.
Climate change is fueling unprecedented warming in marine environments. Crustaceans demonstrate strong physiological responses to rising temperatures including smaller molt increments, more frequent molting, and decreased size-at-maturity (SAM). Despite the potential for these changes to affect population and fisheries dynamics, there is limited research quantifying potential impacts. This is concerning, as crustacean fisheries are becoming increasingly important globally. Using an individual-based model for the valuable American lobster (Homarus americanus) fishery in the Gulf of Maine (GOM), we sought to address pressing questions about how climate-driven changes to growth and maturity could impact the population and fishery dynamics. To do so, we used counterfactual simulations informed by the literature and an expert survey to quantify the effects of smaller
molt increments, increased molting, and decreased SAM on lobster spawning stock biomass (SSB) and landings. We found that all three changes to life history, combined, increased the SSB and landings relative to the base case. Notably, SSB in the terminal year of the time-series was 278.3%, 505.1%, and 748.5% greater than the base
case under small, moderate, and extreme changes, respectively, to life history. However, when molt increment size and molting probability were changed but SAM was not, SSB and landings decreased relative to the base case, emphasizing the importance of SAM as a driver of productivity. Overall, these findings indicate that
climate-driven changes to growth and maturity may favorably impact the population and fishery dynamics of lobster, contributing to sustained fishery yield in the GOM. This study emphasizes the utility of simulating the effects of climate-forced life history change for informing climate-ready fisheries management. Future work should explore the effects of other climate-driven life history changes alongside alternative management strategies for lobster and other crustaceans.
Individual-based models (IBMs) can capture complex processes with a flexible probabilistic approach, which makes them useful for studying organisms with complex life history and fishery processes such as the American lobster (Homarus americanus). This research aims to modify and parameterize an individual-based lobster simulator (IBLS) to simulate the American lobster fishery in the Gulf of Maine. To simulate the fishery, the IBLS was tuned to match the seasonal catch and size composition from the 2015 American lobster stock assessment by adjusting the values of coefficients for select parameters. With appropriate coefficients for the initial abundance, recruitment, and seasonal encounter probability levels, the tuned IBLS accurately simulated the historical landings. Given the uncertainty in future American lobster recruitment, the tuned IBLS was then used to evaluate the effectiveness of current management regulations under different levels of recruitment.
Significance
Climate change is impacting global fisheries and societies that depend on them. Identifying climate adaptation measures requires understanding how environmental changes and management policies interact in driving fishery productivity. Coincident with the recent exceptional warming of the northwest Atlantic Ocean, the American lobster has become the most valuable fishery resource in North America. Here we show that interactions between warming waters, ecosystem changes, and differences in conservation efforts led to the simultaneous collapse of lobster fishery in southern New England and record-breaking landings in the Gulf of Maine. Our results demonstrate that sound, widely adopted fishery conservation measures based on fundamental biological principles can help capitalize on gains and mitigate losses caused by global climate change.
In recent years, the abundance of American lobster Homarus americanus stocks has increased exponentially in coastal Maine, which is likely due to increased recruitment, enhanced growth rates, and decreased predation. This study analyzed the effects of lobster size (12-19.9, 20-29.9, and 30-39.9 mm carapace length, CL) and temperature on growth rates using an 18 yr mark-recapture study in coastal Maine during a period of considerable warming in the Gulf of Maine. Our results showed that the smallest size class of lobsters grew significantly faster than the 2 larger size classes. Peak molt incidence occurred in June and September for all size classes. Greater percent growth measurements were significantly more frequent in warm years for the 12-19.9 mm CL size class, and were also found to be significantly more frequent in the spring season during warm years for all size classes combined. In addition, time at 50% molt probability for the 20-29.9 mm CL and 30-39.9 mm CL size classes was significantly shorter in warm years. This study represents one of the first documentations of growth of small juvenile American lobsters (<20 mm CL) in the wild, and provides evidence of how juvenile growth varies between warm and cold years. Collectively, our findings have implications for how warming sea water temperatures may affect lobster stock productivity, and are of value to lobster stock assessment models and resource management efforts.
It is well known in ecological studies that the choice of spatial scale can influence the possibility of detecting ecological patterns and the type of patterns observed. However, this has rarely been evaluated for fish stock–recruitment (SR) dynamics. Inappropriate scales may result in failure to identify possible SR relationships, especially for species with complicated life history and stock structure and locally generated recruitment. Using American lobster (Homarus americanus) in the Gulf of Maine (GOM) as an example, we tested the hypotheses that the SR relationship is detectable only at certain spatial scales and the functional SR relationships vary with spatial scales. We estimated the SR relationship separately for American lobster in the eastern and western GOM, which have strongly differing oceanographic conditions that may result in different suitable spatial scale and SR dynamics for lobster. We analyzed data of 11 different spatial scales using a Bayesian method. The model fit and performances in the posterior predictive assessment for the SR models were convexly related to the spatial scales. The functional SR relationships differed for different spatial scale. The SR parameter estimates are negatively or concavely related to the spatial scale. The best model was found at medium spatial scale for both the eastern and western GOM, and the scale differed between the eastern and western GOM, suggesting that optimal spatial scale might be process-related. We demonstrated that the choice of spatial scale directly affected the possibility of identifying the SR relationship, the estimation of SR parameters, the type of SR relationships, and the predictive abilities of the SR models.
The Maine lobster Homarus americanus fishery is considered one of the most successful fisheries in the world due in part to its unique comanagement system, the conservation ethic of the harvesters, and the ability of the industry to respond to crises and solve collective‐action problems. However, recent threats raise the question whether the industry will be able to respond to future threats as successfully as it has to ones in the past or whether it is now less resilient and can no longer adequately respond to threats. Through ethnographic research and oral histories with fishermen, we examined the current level of social resilience in the lobster fishery. We concentrated on recent threats to the industry and the ways in which it has responded to them, focusing on three situations: a price drop beginning in 2008, a recovery in 2010–2011, and a second collapse of prices in 2012. In addition, we considered other environmental and regulatory concerns identified by fishermen. We found that the industry is not responding effectively to recent threats and identified factors that might explain the level of social resilience in the fishery.
Received August 20, 2013; accepted October 29, 2014
The spatial distribution of the American lobster Homarus americanus is influenced by many factors, which are often difficult to quantify. We implemented a modeling approach for quantifying season-, size-, and sex-specific lobster spatial distribution in the Gulf of Maine with respect to environmental and spatial variables including bottom temperature, bottom salinity, latitude, longitude, depth, distance offshore, and 2 substratum features. Lobster distribution was strongly associated with temperature and depth, and differed seasonally by sex. In offshore waters in the fall, females were dominant at higher latitudes and males at lower latitudes. This segregation was not apparent in the spring although females were still dominant at higher latitudes in offshore waters. Juveniles and adults were also distributed differently; juveniles were more abundant at the lower latitudes in inshore waters, while adults were more widespread along the entire coast. These patterns are consistent with the ecology of the American lobster. This study provides a tool to evaluate changes in lobster spatial distribution with respect to changes in key habitat and other environmental variables, and consequently could be of value for the management of the American lobster.
The Maine industry for American lobster Homarus americanus has gone from a period of very low catches in the 1920s and 1930s (“the bust”) to a period of “boom” marked by record high catches in the 1990s. Fishers and biologists working for state and federal agencies emphasize different variables in explaining the bust and the boom. What they see as the facts have strong implications for the management of the fishery. Both fishers and biologists believe that a combination of fishing practices and environmental variables have caused the changes in lobster catches observed. However, biologists tend to emphasize the importance of fishing effort and water temperature. Fishers believe that lobster populations have been strongly affected by the way people fish (i.e., by the amount of illegal activity, by restrictions on size and taking of breeding females, etc.), and environmental factors, including predation on lobsters by groundfish, changes in habitat, and what they term “natural cycles.” As a result, biologists are committed to controlling effort; fishers believe the key to management is rules to conserve the breeding stocks directly. Our own analysis of the factors producing the bust and boom leads us to believe that some of the explanations of fishers are folklore, but others should be taken very seriously by managers. These results suggest that fisheries managers should deemphasize reliance on stock–recruitment models; rather, they should manage fisheries by regulating how, when, and where fishing is done.
The egg development index, dry weight, and energy content were measured on eggs from 148 ovigerous female lobsters (Homarus americanus) caught off îles de la Madeleine (Québec). Two modes of embryonic development were observed at stages 3 and 8 (Perkins. 1972. Fish. Bull. 70: 95–99). Stage 3 predominated among females of 71–82 mm and stage 8 among those of 83–110 mm carapace length (CL), indicating that larger females both extrude and hatch their eggs earlier than smaller females. Energy content per egg increased with female size and ranged from 4.6 cal∙egg−1 for females 72–76 mm CL to 5.2 cal∙egg−1 for females 107–110 mm CL. Females between 82 and 90 mm CL invested 0.155 kcal per gram of their own weight in egg production, which was the maximum value in the size range. Females smaller than 82 mm CL and larger than 90 mm CL expended proportionately less on egg production, with the difference allocated to either somatic growth in the smaller or maintenance in the larger animals. Large females produce proportionately more eggs, containing more calories per egg which hatch at an earlier time than small females. The higher energy content of eggs from large females and their earlier hatching are probably factors that enhance larval growth and survival. If so, large females contribute relatively more to recruitment than their greater fecundity.
The American lobster, Homarus americanus, is the most important fishery in the north-east United States. Over the last 20 years, the Collie-Sissenwine (catch-survey) model has been used in estimating fishing mortality in the fishery. This is then compared with a biological reference point derived from an egg-per-recruitment model for determining the status of the stock. However, the complexity of the fishery and population biology for American lobster, data limitations, and uncertainty about underlying parameters call for the develop-ment of stock assessment models with more biological detail. Complex and simple modelling ap-proaches are complementary and both are likely to remain useful for such an important and complex fishery. The objective of this study is to develop a size-structured stock assessment model for the American lobster. The proposed stock assessment model includes a set of size-structured, seasonal, and sex-specific population dynamics models and a sta-tistical approach incorporating data of different sources. Using a fishery simulation based on the information on the lobster fishery in the Gulf of Maine, we evaluated the performance of the pro-posed model in the presence of biased errors in various model variables. This study suggests that the proposed stock assessment model performs well in retrieving the population dynamics of the simulated lobster and is rather robust to the biased errors in growth, fishing selectivity, and landings. Future studies need to focus on the evaluation of the model performance under different scenarios with both biased and random errors.
Unsustainable fishing simplifies food chains and, as with aquaculture, can result in reliance on a few economically valuable species. This lack of diversity may increase risks of ecological and economic disruptions. Centuries of intense fishing have extirpated most apex predators in the Gulf of Maine (United States and Canada), effectively creating an American lobster (Homarus americanus) monoculture. Over the past 20 years, the economic diversity of marine resources harvested in Maine has declined by almost 70%. Today, over 80% of the value of Maine's fish and seafood landings is from highly abundant lobsters. Inflation-corrected income from lobsters in Maine has steadily increased by nearly 400% since 1985. Fisheries managers, policy makers, and fishers view this as a success. However, such lucrative monocultures increase the social and ecological consequences of future declines in lobsters. In southern New England, disease and stresses related to increases in ocean temperature resulted in more than a 70% decline in lobster abundance, prompting managers to propose closing that fishery. A similar collapse in Maine could fundamentally disrupt the social and economic foundation of its coast. We suggest the current success of Maine's lobster fishery is a gilded trap. Gilded traps are a type of social trap in which collective actions resulting from economically attractive opportunities outweigh concerns over associated social and ecological risks or consequences. Large financial gain creates a strong reinforcing feedback that deepens the trap. Avoiding or escaping gilded traps requires managing for increased biological and economic diversity. This is difficult to do prior to a crisis while financial incentives for maintaining the status quo are large. The long-term challenge is to shift fisheries management away from single species toward integrated social-ecological approaches that diversify local ecosystems, societies, and economies.
Ecologists, fisheries scientists, and coastal managers have all called for an ecosystem approach to fisheries management, yet many species such as the American lobster (Homarus americanus) are still largely managed individually. One hypothesis that has yet to be tested suggests that human augmentation of lobster diets via the use of Atlantic herring (Clupea harengus) as bait may contribute to recent increases in lobster landings. Currently 70% of Atlantic herring landings in the Gulf of Maine are used as bait to catch lobsters in traps throughout coastal New England.
We examined the effects of this herring bait on the diet composition and growth rate of lobsters at heavily baited vs. seasonally closed (i.e., bait free) sites in coastal Maine. Our results suggest that human use of herring bait may be subsidizing juvenile lobster diets, thereby enhancing lobster growth and the overall economic value and yield of one of the most valuable fisheries in the U.S.
Our study illustrates that shifting to an ecosystem approach to fisheries management should require consideration of cross-fishery interactions.
This book serves as an advance This book serves as an advanced text on fisheries and fishery population dynamics and as a reference for fisheries scientists. It provides a thorough treatment of contemporary topics in quantitative fisheries science and emphasizes the link between biology and theory by explaining the assumptions inherent in the quantitative methods. The analytical methods are accessible to a wide range of biologists, and the book includes numerous examples. The book is unique in covering such advanced topics as optimal harvesting, migratory stocks, age-structured models, and size models.d text on fisheries and fishery population dynamics and as a reference for fisheries scientists. It provides a thorough treatment of contemporary topics in quantitative fisheries science and emphasizes the link between biology and theory by explaining the assumptions inherent in the quantitative methods. The analytical methods are accessible to a wide range of biologists, and the book includes numerous examples. The book is unique in covering such advanced topics as optimal harvesting, migratory stocks, age-structured models, and size models.
This dissertation research focuses on how environmental (habitat model), ecological (stock-recruitment [SR] model), and economic factors (bioeconomic model) influence the population dynamics of the American lobster, Homarus americanus, in the Gulf of Maine (GOM). Temporal consistency in spatial distribution of lobster at large spatial scales suggests that the distribution may be regulated by environmental variables. I developed a statistical model to estimate season-, size-, and sex-specific lobster spatial distribution in the GOM based on habitat variables. This model is of significant value for American lobster management, providing a basic for predicting how their distribution could respond to environmental variability, an especially important consideration in a region of ongoing changing climate.
It is well known in ecological studies that the choices of spatial scales can influence the possibility of detecting ecological patterns. I tested the hypotheses that the SR relationship for American lobster is detectable only at appropriate spatial scales. The best SR models were found at medium spatial scales but the scales varied for the SR models for eastern and western GOM, which have different oceanic conditions. This suggests that optimal spatial scale might be process-related. I demonstrated that the choice of spatial scale directly affected the possibility of identifying the SR relationship, the estimation of SR parameters, the type of SR relationships, and the predictive abilities of the SR models.
Failure to consider potential behavioral changes of fishers with respect to changes in management initiatives may lead to unintended consequences that do not reflect management goals. I developed a bioeconomic model to evaluate effectiveness of different management strategies under different behavior assumptions of fishers for the Maine lobster fishery. I found that reducing trap limits might actually increase the total number of traps fished unless fishers do not change their behavior in response to trap reduction. Landing tax is robust to changes in fishers’ behavior and also the most effective strategy in terms of fishing effort reduction and harvest schedule modification and most importantly, increases the profit of the fishery. I demonstrated the importance of fishers’ behavior in determining effectiveness of the lobster fishery management.
Twenty-nine percent of trapped nonovigerous females and 69% of trapped ovigerous lobsters were found to be V-notched, during a three-year survey of trap hauls conducted in October 1982-1984 by the Maine Lobstermen's Association. The size-frequency distribution of V-notched lobsters is biased towards larger females relative to that of unmarked females. Calculated numbers of annual eggs per V-notched lobsters were about nine times greater than for unmarked lobsters as a result of their larger size, hence a greater proportion of sexually mature lobsters with higher fecundity. These preliminary results indicate the need to include V-notched lobsters in Maine fishery surveys and assessments and to investigate the possibility of V-notching as a management tool for the Gulf of Maine fishery region.
In total, 7619 v-notched lobsters were released in the Wexford lobster fishery
in Ireland between 1994 and 1999 in order to increase egg production. These
lobsters were legally protected from fishing. Annual reproductive potential
(RP) from these lobsters, based on numbers and size at release, was
2.6×107 eggs. Average ( 95% confidence
limit) standing stock, between 1994 and 1999, from 31 Petersen population
estimates was 29427 3871 female lobsters. Population RP was
6.9×107 eggs per year. After discounting numbers
for natural mortality and incorporating increases in size of surviving
lobsters, RP of v-notched lobsters in 1999 was
4.13×107 eggs per year. Catch rates of v-notched
lobsters were correlated with numbers available for re-capture between 1994
and 1998. In 1999 catch rates were lower than expected, possibly because of
repair and disappearance of the mark during moulting. Catch rates of
undersized lobsters were 37% higher in 1998–99 than in
1994–97.
In highly exploited small-scale lobster fisheries, substantial increases in RP
can be achieved by v-notching. Demonstrating a dependency between local
increases in RP and local recruitment is problematic and requires more
information on the early life history and the recruitment process.
The remarkable increase of Homarus Americanus (lobster) abundance in recent years has resulted in record landings throughout the states and provinces along the perimeter of the Gulf of Maine. A considerable amount of data on various life stages of lobsters has been collected for research, management and conservation purposes over the past 15 years. We have used these data sets to develop models that simulate lobster populations from newly hatched larval stage through settlement and recruitment to the fishery. This paper presents a part of the synthesis study that focuses on the early life history of lobsters.A coupled biophysical individual based model was developed that considers patterns of egg production (abundance, distribution and timing of hatch), temperature-dependent larval growth, stage-explicit vertical distributions of larvae, and mortality. The biophysical model was embedded in the realistic simulations of the physical environment (current and temperature) from the Gulf of Maine Nowcast/Forecast System. The predominant direction of larval movement follows the cyclonic Gulf of Maine Coastal Current (GMCC). Results show relatively low accumulation of planktonic stages along the eastern Maine coast and high accumulation along the western Maine coast. In years when the eastern branch of the GMCC turns offshore southeast of Penobscot Bay, more particles accumulate downstream of the branch point. Interannual variability is also apparent in development times that vary as a function of year-to-year water temperature variation. The larval stages tend to remain relatively near shore, but the final planktonic stage (the postlarva) resides near the sea surface, and the prevailing southwesterly winds in summer cause eastward and offshore drift of postlarvae. Thus, more settlement might take place earlier in the potentially long postlarval stage, and the timing and strength of the southwesterly winds are important in determining the population of potential settlers.
The American lobster, Homarus americanus, is abundant
(>1/m2) in spatially complex coastal habitats of
the Gulf of Maine. Quadrat surveys (stratified by exposure, depth, and
substrate) conducted at fixed locations since 1989 revealed consistently
higher lobster population densities west and south of Penobscot Bay in central
Maine. High-resolution surveys in 1999 at 70 closely spaced dive sites
revealed distinct settlement hot spots and cold spots, stable over several
years at least. Densest settlement occurred along a 100-km outer coastal
region westward from the mouth of Penobscot Bay. A settlement cold spot about
60-km in diameter was evident in the north-east corner of Penobscot Bay.
Abundance of older, adolescent-phase, lobsters (40–90 mm carapace
length, CL) corresponded with patterns of settlement. Catch rates per trap
haul of prerecruits (< 83 mm CL) and catch rates per area for lobsters
fully recruited to the fishery (83 mm CL) correspond with local lobster
densities. Until recently, populations increased in three of four regions over
the past decade, most strongly in north-eastern Maine. Landings per length of
coastline corresponded to spatial and temporal patterns of abundance.
Consistent spatial and temporal patterns suggest that population densities can
be reliably determined from calibrated fisherydependent data.
Demersal fishes are widely thought to be an important source of natural mortality for juvenile American lobster Homarus americanus. There were no significant relationships between abundance indices of American lobster and the dominant demersal fish species, Atlantic cod Gadus morhua, in the southern Gulf of St. Lawrence. American lobster was found in only one of 22,625 Atlantic cod stomachs collected between 1955 and 1980—a period of low American lobster abundance. Only six of 12,008 Atlantic cod collected between July 1990 and October 1996 (a period of high American lobster abundance) had eaten American lobster. Most size-classes of the two species were spatially separate from early July to early September and November to May. American plaice Hippoglossoides platessoides, the second most abundant demersal fish species, did not eat American lobster (n = 1,800 stomachs). Again, the two species were spatially isolated for most of the year. More limited studies (in terms of spatial or seasonal coverage) on the diets of eight shallow-water fish species (n = 4,674 stomachs) detected consumption of American lobster by shorthorn sculpin Myoxocephalus scorpius, cunner Tautogolabrus adspersus, and white hake Urophysis tenuis but not by winter flounder Pleuronectes americanus, yellowtail flounder P. ferruginea, thorny skate Raja radiata, spiny dogfish Squalus acanthias, or Greenland cod Gadus ogac. This study eliminated Atlantic cod, Greenland cod, American plaice, yellowtail flounder, winter flounder, and thorny skate as important predators of American lobster in the southern Gulf of St. Lawrence; however, the question of which of the remaining demersal fish species are important predators of American lobster remains largely unresolved.
Sustainable fisheries are hard to find. Even harder to find are communities that take full responsibility for their own resources. Fishermen in Eastport Peninsula, Newfoundland, Canada have begun a comprehensive conservation initiative to increase and preserve the Lobster resource upon which they depend. The initiative, including measures to increase egg production, also explores the efficacy of no-take reserves. The initiative is working and spreading to other communities. Peer-reviewed article accepted for publication on 11 February 2002.
A stock-recruitment relationship (SRR) between the spring spawning stock levels and the following autumn recruitment has been established for P. esculentus in Exmouth Gulf. The basic SRR fits the data well with the exception of 2 out of the 14 years when particularly severe cyclones occurred. This has been taken into account by using multiple regression techniques to incorporate the amount of rainfall in January and February as variables representing indices of cyclone activity (multiple correlation of 0.97). An hypothesis for the observed positive and negative effects of cyclones on recruit survival has been presented. The relationship between autumn recruitment and resultant spring spawning stock (RSR) later that year and the effects of fishing, measured in effective effort units, has also been established (multiple correlation of 0.94). An examination of the interaction between the SRR and RSR relationships has been reported which suggests that, under average environmental conditions and high levels of effort, recruitment will move towards a new lower equilibrium level. The robustness of the relationships with respect to assumptions involved and potential sources of bias in the variables used have been evaluated and discussed.
Mammalian carnivores are particularly vulnerable to extinction in fragmented landscapes, and their disappearance may lead to increased numbers of smaller carnivores that are principle predators of birds and other small vertebrates. Such `mesopredator release' has been implicated in the decline and extinction of prey species. Because experimental manipulation of carnivores is logistically, financially and ethically problematic,, however, few studies have evaluated how trophic cascades generated by the decline of dominant predators combine with other fragmentation effects to influence species diversity in terrestrial systems. Although the mesopredator release hypothesis has received only limited critical evaluation and remains controversial, it has become the basis for conservation programmes justifying the protection of carnivores. Here we describe a study that exploits spatial and temporal variation in the distribution and abundance of an apex predator, the coyote, in a landscape fragmented by development. It appears that the decline and disappearance of the coyote, in conjunction with the effects of habitat fragmentation, affect the distribution and abundance of smaller carnivores and the persistence of their avian prey.
We examined relationships between successive life history stages of an American lobster (Homarus americanus) population for evidence of density-dependent control. Analysis of a time series of larval production estimates for the Northumberland Strait region of the southern Gulf of St. Lawrence during 1949–63 (D. J. Scarratt. 1964. J. Fish. Res. Board Can. 21: 661–680; D. J. Scarratt. 1973. J. Fish. Res. Board Can. 30: 1819–1824) provided no indication of density-dependent regulation during the pelagic larval phase. However, an asymptotic relationship between the final (fourth) larval stage and stock size 5–7 yr later was demonstrated, indicating the possibility of density-dependent regulation between larval settlement and subsequent recruitment to the fishery. A second analysis supported these results based on trends in population size over several generations. A recruitment mechanism of this type is highly stabilizing and can explain the apparent capacity of lobster populations to sustain high levels of fishing mortality. The postulated recruitment mechanism for Northumberland Strait lobsters may reflect competition for critical resources. We propose that shelter is an important limiting resource and that shelter competition experiments be undertaken in the field and laboratory to test this hypothesis. Finally, we demonstrate the use of a multistage recruitment model which accounts for the general form of observed interstage relationships. The asymptotic relationship between stage IV production and subsequent stock results in a stable population which is resilient to exploitation.
New information on female size at maturity, fecundity, and relative egg production per recruit is presented for American lobsters (Homarus americanus) from three areas in the Canadian Maritimes. Based on pleopod examination, sizes at 50% maturity for females were estimated at 108.1 mm carapace length (CL) from the Fundy area (Bay of Fundy and southwestern Nova Scotia), at 92.5 mm CL from eastern Nova Scotia, and at 78.5 mm CL from Northumberland Strait. There was a curvilinear relationship between the number of eggs per female and CL. An egg-per-recruit model predicted that in all three areas the second and third molt groups beyond the legal minimum recruit size contribute the most to egg production under current exploitation rates. Lobsters in Northumberland Strait and eastern Nova Scotia produce up to 30–50% of their eggs at sizes smaller than those at which females from the Bay of Fundy start to produce eggs. Although the stock–recruitment relationships for H. americanus are unknown, the egg-per-recruit assessment suggests that all three areas would benefit in egg production increases by increasing minimum legal recruit size by one molt increment.
Using numerical models, effects of environmental variability upon yield were tested for six single-age fish stocks characterized by different kinds and degrees of density-dependent reproduction potential. The two levels of variability examined had extremes of yield standing in the ratios 7:1 and 18:1, respectively. Close regulation of fishing to the optimum percentage for each year's stock improves the long-term average catch taken, the improvement being the greater, the more variable the environment. With the higher level of variability, improvement in average catch among five of the stocks ranged from 26% to 79% increase. However this increase in mean catch is achieved at the expense of increased variability in catch from year to year—in fact, for some kinds of stocks there must be complete cessation of fishing in some years in order to get the long-term maximum. The yield of stocks, in which reproduction per spawner declines at low levels of abundance, is particularly improved by a close adaptation of fishing effort to the supply of fish available.When two or more populations of a species, characterized by different reproduction potentials, are fished in common, total potential catch is less than when each can be fished separately at its optimum level. If a common fishery cannot be avoided, the achievement of maximum average yield may find one of two originally-equal stocks as abundant or even more abundant than before the fishery began, while the other may persist only at a low level or even be exterminated completely.
Currently, one of the most important issues in resource management is: under what conditions will people conserve the resources on which their livelihood depends? In all too many cases, overexploitation is the rule. All around the world fish stocks, forests, grasslands, air, soils, wildlife, and water quality have been seriously degraded by human beings. Environmental disaster is not inevitable, however, for in many cases those who are dependent on resources, and their governments, have acted to generate effective rules to manage those resources at sustainable levels (Anderson and Simmons 1993; Berkes 1989; McCay and Acheson 1987; Ostrom 1990; Pinkerton 1989; Ruddle and Akimichi 1984).
Plotting net reproduction (reproductive potential of the adults obtained) against the density of stock which produced them, for a number of fish and invertebrate populations, gives a domed curve whose apex lies above the line representing replacement reproduction. At stock densities beyond the apex, reproduction declines either gradually or abruptly. This decline gives a population a tendency to oscillate in numbers; however, the oscillations are damped, not permanent, unless reproduction decreases quite rapidly and there is not too much mixing of generations in the breeding population. Removal of part of the adult stock reduces the amplitude of oscillations that may be in progress and, up to a point, increases reproduction.
Natural resources of all kinds have been overexploited by user groups who cannot or will not develop rules to constrain their own exploitive efforts. One notable exception is the Maine lobster industry, where an effective set of conservation laws has been developed due, in great part, to the strong support of the industry. In the early decades of the 20th century, however, the lobster industry was marked by widespread violations of the existing conservation laws and opposition to developing more. This article explores the way that the pirate ethic gave way to the conservation ethic in the 1930s. Our explorations in evolutionary game theory suggest that this change was produced by three factors: costs and benefits of defection from the conservation ethic; numbers of people accepting the conservation ethic quality rule; and events that shocked the system from one state to another. We argue that the shock to the system in the late 1920s and 1930s was caused by massive stock failure which changed the attitudes of many fishermen about the need for conservation. People began to report violations of the law, which made law enforcement more effective and quickly led to a cascade of fishermen abandoning the pirate ethic. In the late 1930s, increasing catches, in combination with a number of other social, technical, and economic factors continued the upward spiral.
Community-based conservation (CBC) is based on the idea that if conservation and development could be simultaneously achieved, then the interests of both could be served. It has been controversial because community development objectives are not necessarily consistent with conservation objectives in a given case. I examined CBC from two angles. First, CBC can be seen in the context of paradigm shifts in ecology and applied ecology. I identified three conceptual shifts-toward a systems view, toward the inclusion of humans in the ecosystem, and toward participatory approaches to ecosystem management-that are interrelated and pertain to an understanding of ecosystems as complex adaptive systems in which humans are an integral part. Second, I investigated the feasibility of CBC, as informed by a number of emerging interdisciplinary fields that have been pursuing various aspects of coupled systems of humans and nature. These fields-common property, traditional ecological knowledge, environmental ethics, political ecology, and environmental history-provide insights for CBC. They may contribute to the development of an interdisciplinary conservation science with a more sophisticated understanding of social-ecological interactions. The lessons from these fields include the importance of cross-scale conservation, adaptive comanagement, the question of incentives and multiple stakeholders, the use of traditional ecological knowledge, and development of a cross-cultural conservation ethic.
Marine fisheries are in a state of crisis. One of the few successfully managed fisheries is the Maine lobster industry where catches are at an all time high. An important factor in this success is the effectiveness of regulations which were developed during three periods over the course of the past 125 years. In all cases, the regulations are the result of heavy lobbying activity by various factions in the industry. Both strong commercial rivalry and genuine concern for the well-being of the lobster resource played a role in generating these regulations. However, history did not repeat itself. In each period, the players, circumstances, and goals were very different. The result, however, is a set of effective regulations which are largely self-enforcing.
This paper provides the first ex post estimates of the effects of input controls on technical efficiency in a fishery. Using individual vessel data from the northern prawn fishery of Australia for the years 1990-1996 and 1994-2000, stochastic production frontiers are estimated to analyse the efficiency impacts of input controls on engine and vessel size. The results indicate that technical efficiency is increasing in a measure of vessel size and engine capacity that was controlled by the regulator from 1985 to 2001, and decreasing in an unregulated input, gear headrope length. The study shows that fishers have substituted from regulated to unregulated inputs over the period 1990-2000 and technical efficiency has declined coincident with increasing restrictions on vessel size and engine capacity. The decline in technical efficiency indicates that the goal of the regulator to increase economic efficiency has not been realized.
Using homologous molecular probes, we examined the influence of equivalent temperature shifts on the in vivo expression of genes coding for a constitutive heat shock protein (Hsc70), heat shock proteins (Hsps) (Hsp70 and Hsp90), and polyubiquitin, after acclimation in the American lobster, Homarus americanus. We acclimated sibling, intermolt, juvenile male lobsters to thermal regimes experienced during overwintering conditions (0.4 +/- 0.3 degrees C), and to ambient Pacific Ocean temperatures (13.6 +/- 1.2 degrees C), for 4-5 weeks. Both groups were subjected to an acute thermal stress of 13.0 degrees C, a temperature shift previously found to elicit a robust heat shock response in ambient-acclimated lobsters. Animals were examined after several durations of acute heat shock (0.25-2 hours) and after several recovery periods (2-48 hours) at the previous acclimation temperature, following a 2-hour heat shock. Significant inductions in Hsp70, Hsp90, and polyubiquitin messenger RNA (mRNA) levels were found for the ambient-acclimated group. Alternatively, for the cold-acclimated group, an acute thermal stress over an equivalent interval resulted in no induction in mRNA levels for any of the genes examined. For the ambient-acclimated group, measurements of polyubiquitin mRNA levels showed that hepatopancreas, a digestive tissue, incurred greater irreversible protein damage relative to the abdominal muscle, a tissue possessing superior stability over the thermal intervals tested.
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