Course corrections responding to climate impacts produce divergent effects on population biomass and harvest in fisheries

Background. The ongoing climatic changes have a significant impact on the fishing resources of the Azov Sea. Relevance. Due to the depressed state of the stocks of traditional fishing targets, it is urgent to search for alternative ones that can compensate for the shrinking catches and ensure the development of fishing in new environmental conditions. The aim of this work was to assess the abundance and biomass dynamics of the pontogammarus in the context of the increasing salinity. Methods. This work is based on the data collected over the course of the 2001–2023 studies on the assessment of the abundance and biomass of the pontogammarus population in the Azov Sea, taking into account the habitat parameters (namely, salinity). The pontogammarus samples were collected in the supralittoral zone with a benthic frame and a sampling trap, and in the upper sublittoral zone at a depth of 0.5 m with a trap. The samples were fixed with 4 % aqueous formaldehyde solution. The laboratory processing included the determination of the species, sex, dimensional characteristics, the number of individuals in the sample, and the individual weight of the crustaceans. Results. In 2001–2015, within the salinity range of 9.64–13.24 ‰, an increase in the specific abundance and biomass of the population was recorded in the Azov Sea. A significant positive relationship was found between the specific abundance, specific biomass and salinity of the sea (r=0.87–0.91). A further increase in the salinity to 14.91–15.29 ‰ in 2021–2023 had an adverse effect on the density of crustacean distribution as compared to that in 2015. Correlation analysis revealed a strong negative relationship (r=-0.99) between the salinity and the number of crustaceans in the aggregations, as well as their biomass. In Taganrog Bay, at a salinity of 5.26–7.34 ‰, the abundance and biomass had the lowest values compared to the entire area of the Azov Sea. With the increase in the salinity in 2009–2015, there was also recorded an increase in the specific abundance and biomass of the pontogammarus. A strong positive relationship (r=0.90–0.92) was identified between quantitative indicators of population distribution and water salinity. In subsequent years (2021–2023), the relationship between the quantitative characteristics of the pontogammarus population and the salinity in the bay remained positive. Conclusion. The water salinity in the range of 11.25–13.24 ‰ is optimal for the vital activity of pontogammarus; it is the level at which the aggregations with the highest abundance and biomass can be formed. If the water salinity of the Azov Sea continues to increase, in the following years, a decrease in the abundance and biomass of crustacean aggregations is expected, which will lead to the reduction in the total stock of this exploitable resource.

Efficacy of fisheries management strategies in mitigating ecological, social, and economic risks of climate warming in China.

Marine reserve networks are increasingly implemented to conserve biodiversity and enhance the persistence and resilience of exploited species and ecosystems. However, the efficacy of marine reserve networks in frequently disturbed systems, such as coral reefs, has rarely been evaluated. Here we analyze a well-mixed larval pool model and a spatially explicit model based on a well-documented coral trout (Plectropomus spp.) metapopulation in the Great Barrier Reef Marine Park, Australia, to determine the effects of marine reserve coverage and placement (in relation to larval connectivity and disturbance heterogeneity) on the temporal stability of fisheries yields and population biomass in environmentally disturbed systems. We show that marine reserves can contribute to stabilizing fishery yield while increasing metapopulation persistence, irrespective of whether reserves enhance or diminish average fishery yields. However, reserve placement and the level of larval connectivity among subpopulations were important factors affecting the stability and sustainability of fisheries and fish metapopulations. Protecting a mix of disturbed and non-disturbed reefs, rather than focusing on the least-disturbed habitats, was the most consistently beneficial approach across a range of dispersal and reserve coverage scenarios. Placing reserves only in non-disturbed areas was the most beneficial for biomass enhancement, but had variable results for fisheries and could potentially destabilize yields in systems with well-mixed larval or those that are moderately fished. We also found that focusing protection on highly disturbed areas could actually increase variability in yields and biomass, especially when degraded reef reserves were distant and poorly connected to the meta-population. Our findings have implications for the design and implementation of reserve networks in the presence of stochastic, patchy environmental disturbances.

Stocking strategies for a pre-alpine whitefish population under temperature stress

Coastal embayments are at risk of impacts by climate change drivers such as ocean warming, sea level rise and alteration in precipitation regimes. The response of the ecosystem to these drivers is highly dependent on their magnitude of change, but also on physical characteristics such as bay morphology and river discharge, which play key roles in water residence time and hence estuarine functioning. These considerations are especially relevant for bivalve aquaculture sites, where the cultured biomass can alter ecosystem dynamics. The combination of climate change, physical and aquaculture drivers can result in synergistic/antagonistic and nonlinear processes. A spatially explicit model was constructed to explore effects of the physical environment (bay geomorphic type, freshwater inputs), climate change drivers (sea level, temperature, precipitation) and aquaculture (bivalve species, stock) on ecosystem functioning. A factorial design led to 336 scenarios (48 hydrodynamic×7 management). Model outcomes suggest that the physical environment controls estuarine functioning given its influence on primary productivity (bottom-up control dominated by riverine nutrients) and horizontal advection with the open ocean (dominated by bay geomorphic type). The intensity of bivalve aquaculture ultimately determines the bivalve-phytoplankton trophic interaction, which can range from a bottom-up control triggered by ammonia excretion to a top-down control via feeding. Results also suggest that temperature is the strongest climate change driver due to its influence on the metabolism of poikilothermic organisms (e.g. zooplankton and bivalves), which ultimately causes a concomitant increase of top-down pressure on phytoplankton. Given the different thermal tolerance of cultured species, temperature is also critical to sort winners from losers, benefiting Crassostrea virginica over Mytilus edulis under the specific conditions tested in this numerical exercise. In general, it is predicted that bays with large rivers and high exchange with the open ocean will be more resilient under climate change when bivalve aquaculture is present.

Climate-driven shifts in growth and maturity induce changes to the population and fishery dynamics of a high-value crustacean

Catchments in the future North: interdisciplinary science for sustainable management in the 21^st Century

Interactive effects of multiple climate change variables on food web dynamics: Modeling the effects of changing temperature, CO2, and water availability on a tri-trophic food web

Mutualistic interactions are regulated by plant and animal traits, including animal body size and population density. In seed dispersal networks, frugivore body size determines the interaction outcome, and species population density determines interaction probability through encounter rates. To date, most studies examining the relative role of body size and population density in seed dispersal networks have examined animal guilds encompassing a narrow range of body sizes (e.g., birds only). Given non-random, body-size dependent defaunation, understanding the relative role of these traits is important to predict and, ideally, mitigate the effects of defaunation. We analyzed a hyper-diverse seed dispersal network composed of birds and mammals that cover a wide range of body sizes and population densities in the Brazilian Pantanal. Animal density per se did not significantly explain interaction patterns. Instead, population biomass, which represents the combination of body size and population density, was the most important predictor for most interaction network metrics. Population biomass was strongly correlated with body size, but not with density. Thus, larger frugivore species dispersed more plant species and were involved in more unique pairwise interactions than smaller species. Moreover, species with larger population biomass had the strongest influence (i.e., as indicated by measures of centrality) on other species in the network and were more generalist, interacting with a broader set of species, compared to species with lower population biomass. We posit that the increased abundance of small-sized frugivores resulting from the pervasive defaunation of large vertebrates would not compensate for the loss-of-function of the latter and the inherent disruption of seed dispersal networks.

An age-structured model for erratic crappie fisheries

Many jurisdictions are currently pursuing renewable sources of energy from the ocean, including offshore wind farms (OWFs). While these could have direct positive effects for global climate change by reducing fossil fuel consumption, there could be unintended consequences for fisheries and conservation. These include the potential loss of fishing grounds (and the consequent spatial displacement of fishing effort) and the potential loss of fishery‐independent survey data in OWF areas. Because fishing and other types of vessel traffic are often limited in the OWF area, OWFs may also serve as other effective area‐based conservation measures (OECMs), an important type of spatial protection in the context of the Convention on Biological Diversity 30 × 30 initiative. We used spatially explicit population models of groundfish fisheries on an idealized coastline in a management strategy evaluation to investigate the effects of OWF placement on conservation objectives (increased fish biomass) and fishery objectives (maintaining fishery yield). We simulated the loss of fishing grounds on 10% of the coastline, and the concurrent loss of 10% of fishery‐independent survey data, introducing uncertainty and bias into stock status estimates. This produced two effects in the model: initial loss of fishery yield due to the closure and reductions in fishing effort when the loss of data triggered precautionary measures in the harvest control rule. Additionally, we assessed scenarios with different placements of the OWF relative to high‐quality fish habitat, as OWFs could be placed without fish habitat considerations in mind. As expected (given the sustainable harvest rates we simulated), we found that placing the OWF on high‐quality habitat produced the greatest negative effects of fishing grounds and fishery‐independent data on fishery yields, but placing the OWF on low‐quality habitat caused it to be ineffective as an OECM (in terms of increasing fish population biomass). Additionally, the loss of survey data had a greater effect for less mobile fish species. Our findings highlight the expected trade‐offs between the fishery and conservation (i.e., OECM) consequences of OWF expansion and the need to compensate for the loss of fishery‐independent data by accounting for species distributions relative to habitat in survey indices.

Sustained Antarctic Research: A 21st Century Imperative

Spatial partitioning between species of the phytoplankton-feeding guild on an estuarine intertidal sand flat and its implication on habitat carrying capacity

Extension of fisheries jurisdiction by Canada in January 1977 radically changed management practices in a large part of the northwestern Atlantic. Management regimes before and after 1977 are described, and trends in fish catches and resource abundance are analyzed. In the Canadian zone, both nominal catches and population biomass decreased by 50% between the late 1960s and the mid-1970s. After 1977, catches stabilized at early 1960s levels (i.e., levels before major expansion of the international fishery in the area) and overall population biomass increased to late 1960s levels. The reversal in population trends corresponds with major changes in fishing practices, particularly the substantial reduction in fishing mortality. However, it has also been proposed that large-scale environmental factors have had an important influence on resource trends.

Complex spatial structure is widely viewed as an attribute that can contribute to stability in fish populations. Depending on aspects of stock demography and productivity, the existence of complete or partial spatial refugia can enable population persistence when faced with high rates of exploitation. The Southern Flounder Paralichthys lethostigma has been harvested extensively by inshore fisheries in North Carolina for more than three decades, with estimates of fishing mortality (F) surpassing 2.0 year−1 in several years and systems. Potential hypotheses to explain population persistence under heavy exploitation include high levels of recruitment at low stock sizes (high steepness) and/or the maintenance of adult biomass in offshore habitats that remain cryptic to the fishery. We constructed and applied an age-structured matrix model to evaluate the potential for cryptic stock structure, combined with varying levels of steepness in the stock–recruit relationship, to sustain the Southern Flounder stock across a range of plausible exploitation scenarios. Model simulations predicted that both high steepness in the stock–recruit relationship and large fractions of cryptic biomass were necessary to maintain even modest levels (~25%) of unfished biomass at the high estuarine harvest rates that have likely occurred since the inception of the fishery. When the estuarine fishery exploited the stock at an elevated rate (F > 1.0), high steepness in the stock–recruit relationship alone was insufficient to maintain population biomass at sustainable levels. Only maintaining a large fraction of the adult stock within the spatial refuge afforded by offshore habitats could offset high rates of estuarine exploitation and maintain more conservative levels (40% of unfished biomass) of population biomass. Future efforts should be focused on the identification and preservation of spatial structure within the Southern Flounder stock to maintain both age structure and fishery yield.