skip to main content

Title: Projecting the timescale of initial increase in fishery yield after implementation of marine protected areas
Abstract Adaptive management of marine protected areas (MPAs) to determine whether they are meeting their intended goals requires predicting how soon those goals will be realized. Such predictions have been made for increases in fish abundance and biomass inside MPAs. However, projecting increases in fishery yield (“fishery spillover”) is more complex because it involves both how the fishery is managed and uncertainty in larval connectivity. We developed a two-patch, age-structured population model, based on a renewal equation approach, to project the initial timing of increase in fishery yield from larvae exported from a no-take MPA. Our results link our understanding of the predicted timing of increases in biomass (and thus reproduction) in MPAs with the time-lags associated with new recruits entering the fishery. We show that the time-lag between biomass peaking within the MPA and the increased fishery yield outside the MPA reaching its maximum depends, in a predictable way, on the age-dependent patterns of growth, natural mortality, and fishing mortality. We apply this analysis to 16 fishery species from the US Pacific coast; this difference ranged from 7 to 18 years. This model provides broadly applicable guidance for this important emerging aspect of fisheries management.
; ; ;
Anderson, Emory
Award ID(s):
Publication Date:
Journal Name:
ICES Journal of Marine Science
Page Range or eLocation-ID:
1860 to 1871
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Marine Protected Areas (MPAs) are being implemented worldwide, yet there are few cases where managers make specific predictions of the response of previously harvested populations to MPA implementation.

    Such predictions are needed to evaluate whether MPAs are working as expected, and if not, why. This evaluation is necessary to perform adaptive management, identifying whether and when adjustments to management might be necessary to achieve MPA goals.

    Using monitoring data and population models, we quantified expected responses of targeted species to MPA implementation and compared them to monitoring data.

    The model required two factors to explain observed responses in MPAs: (a) pre‐MPA harvest rates, which can vary at local spatial scales, and (b) recruitment variability before and after MPA establishment. Low recruitment years before MPA establishment in our study system drove deviations from expected equilibrium population size distributions and introduced an additional time lag to response detectability.

    Synthesis and applications. We combined monitoring data and population models to show how (a) harvest rates prior to Marine Protected Area (MPA) implementation, (b) variability in recruitment, and (c) initial population size structure determine whether a response to MPA establishment is detectable. Pre‐MPA harvest rates across MPAs plays a large role in MPA response detectability, demonstrating themore »importance of measuring this poorly known parameter. While an intuitive expectation is for response detectability to depend on recruitment variability and stochasticity in population trajectories after MPA establishment, we address the overlooked role of recruitment variability before MPA establishment, which alters the size structure at the time of MPA establishment. These factors provide MPA practitioners with reasons whether or not MPAs may lead to responses of targeted species. Our overall approach provides a framework for a critical step of adaptive management.

    « less
  2. Abstract

    Most fishing is inherently size‐selective, in that fishers preferentially select a subset of the population for harvest based on economic incentives associated with different‐sized fish. Size‐selective fishing influences the targeted population and fishery performance in multiple ways, including changing the reproductive capacity of the target population and altering fishery yield. Understanding how social–ecological variability, including size selectivity, affects target species populations is critical for fisheries management to optimize the benefits of fisheries and the ecological impacts on target populations. In this study, we used yield per recruit, spawning stock biomass per recruit, and length‐based spawning potential ratio models to explore how a range of size selectivity scenarios affect fishery and population productivity for Mexican chocolate clams,Megapitaria squalida, in Loreto, Baja California Sur, Mexico. We found that alternate slot limits result in trade‐offs between fishery yield and reproductive productivity of the target population. A more restrictive slot limit reduced the proportion of the population available to harvest, resulting in higher reproductive capacity of the population, compared to a less restrictive slot limit, conditional on the rate of fishing mortality. In the long run, a more restrictive slot limit will likely lead to a higher number of recruits, larger stock size,more »and higher long‐term fishery yield relative to a less restrictive scenario. Our findings highlight that how people fish matters, perhaps as much as the quantity of fish harvested; size‐selective fishing that aligns with the life history of target populations and stakeholders’ goals is critical to sustaining fisheries and the valuable food and livelihoods they provide.

    « less
  3. Marine protected areas (MPAs) are among the most widely used strategy to protect marine ecosystems and are typically designed to protect specific habitats rather than a single and/or multiple species. To inform the con- servation of species of conservation concern there is the need to assess whether existing and proposed MPA designs provide protection to these species. For this, information on species spatial distribution and exposure to threats is necessary. However, this information if often lacking, particularly for mobile migratory species, such as marine turtles. To highlight the importance of this information when designing MPAs and for assessments of their effectiveness, we identified high use areas of post-nesting hawksbill turtles (Eretmochelys imbricata) in Brazil as a case study and assessed the effectiveness of Brazilian MPAs to protect important habitat for this group based on exposure to threats. Most (88%) of high use areas were found to be exposed to threats (78% to artisanal fishery and 76.7% to marine traffic), where 88.1% were not protected by MPAs, for which 86% are exposed to threats. This mismatch is driven by a lack of explicit conservation goals and targets for turtles in MPA management plans, limited spatial information on species' distribution and threats,more »and a mismatch in the scale of conservation initiatives. To inform future assessments and design of MPAs for species of conservation concern we suggest that managers: clearly state and make their goals and targets tangible, consider ecological scales instead of political boundaries, and use adaptative management as new information become available.« less
  4. Abstract Marine Protected Areas (MPAs) are designed to enhance biodiversity and ecosystem services. Some MPAs are also established to benefit fisheries through increased egg and larval production, or the spillover of mobile juveniles and adults. Whether spillover influences fishery landings depend on the population status and movement patterns of target species both inside and outside of MPAs, as well as the status of the fishery and behavior of the fleet. We tested whether an increase in the lobster population inside two newly established MPAs influenced local catch, fishing effort, and catch-per-unit-effort (CPUE) within the sustainable California spiny lobster fishery. We found greater build-up of lobsters within MPAs relative to unprotected areas, and greater increases in fishing effort and total lobster catch, but not CPUE, in fishing zones containing MPAs vs. those without MPAs. Our results show that a 35% reduction in fishing area resulting from MPA designation was compensated for by a 225% increase in total catch after 6-years, thus indicating at a local scale that the trade-off of fishing ground for no-fishing zones benefitted the fishery.
  5. Abstract

    Size‐based harvest limits or gear regulations are often used to manage fishing mortality and ensure the spawning biomass of females is sufficiently protected. Yet, management interactions with species’ mating systems that affect fishery sustainability and yield are rarely considered. For species with obligate male care, it is possible that size‐specific harvest of males will decrease larval production. In order to examine how size‐based management practices interact with mating systems, we modelled fisheries of two species with obligate care of nests, corkwing wrasse (Symphodus melops, Labridae) and lingcod (Ophiodon elongatus,Hexigrammidae) under two management scenarios, a minimum size limit and a harvest slot limit. We simulated the population dynamics, larval production and yield to the fishery under a range of fishing mortalities. We also modelled size‐dependent male care to determine its interaction with management. In both species, the slot limit decreased yield by <12% (relative to minimum size limits) at low fishing mortalities; at higher mortalities, individuals rarely survived to outgrow the slot and spawning potential decreased substantially relative to unfished levels, similar to minimum size limits. Spawning potential decreased less when managed with a slot limit if we included a positive feedback between male size, care and hatching success, butmore »the benefit of implementing the slot depended both on the relative proportions of each sex selected by the fishery and on our assumptions regarding male size and care. This work highlights that the effects of size‐ and sex‐selective fisheries management can be nuanced and produce counter‐intuitive results.

    « less