Half a century of global decline in oceanic sharks and rays

This is the author accepted manuscript. The final version is available from Nature Research via the DOI in this recordData availability: Data are available on https://www.sharkipedia.org/ and at https://doi.org/10.5281/zenodo.4135325. Source data are provided with this paper.Overfishing is the primary cause of marine defaunation, yet declines in and increasing extinction risks of individual species are difficult to measure, particularly for the largest predators found in the high seas. Here we calculate two well-established indicators to track progress towards Aichi Biodiversity Targets and Sustainable Development Goals: the Living Planet Index (a measure of changes in abundance aggregated from 57 abundance time-series datasets for 18 oceanic shark and ray species) and the Red List Index (a measure of change in extinction risk calculated for all 31 oceanic species of sharks and rays). We find that, since 1970, the global abundance of oceanic sharks and rays has declined by 71% owing to an 18-fold increase in relative fishing pressure. This depletion has increased the global extinction risk to the point at which three-quarters of the species comprising this functionally important assemblage are threatened with extinction. Strict prohibitions and precautionary science-based catch limits are urgently needed to avert population collapse, avoid the disruption of ecological functions and promote species recovery.Shark Conservation FundUS National Science FoundationAustralian Government National Environmental Science ProgramNatural Science and Engineering Research CouncilCanada Research Chairs Progra

Ecological and evolutionary consequences of alternative sex-change pathways in fish

Sequentially hermaphroditic fish change sex from male to female (protandry) or vice versa (protogyny), increasing their fitness by becoming highly fecund females or large dominant males, respectively. These life-history strategies present different social organizations and reproductive modes, from near-random mating in protandry, to aggregate- and harem-spawning in protogyny. Using a combination of theoretical and molecular approaches, we compared variance in reproductive success (V k*) and effective population sizes (N e) in several species of sex-changing fish. We observed that, regardless of the direction of sex change, individuals conform to the same overall strategy, producing more offspring and exhibiting greater V k* in the second sex. However, protogynous species show greater V k*, especially pronounced in haremic species, resulting in an overall reduction of N e compared to protandrous species. Collectively and independently, our results demonstrate that the direction of sex change is a pivotal variable in predicting demographic changes and resilience in sex-changing fish, many of which sustain highly valued and vulnerable fisheries worldwide

Female reproductive competition explains variation in prenatal investment in wild banded mongooses

PublishedArticleFemale intrasexual competition is intense in cooperatively breeding species where offspring compete locally for resources and helpers. In mammals, females have been proposed to adjust prenatal investment according to the intensity of competition in the postnatal environment (a form of ‘predictive adaptive response’; PAR). We carried out a test of this hypothesis using ultrasound scanning of wild female banded mongooses in Uganda. In this species multiple females give birth together to a communal litter, and all females breed regularly from one year old. Total prenatal investment (size times the number of fetuses) increased with the number of potential female breeders in the group. This relationship was driven by fetus size rather than number. The response to competition was particularly strong in low weight females and when ecological conditions were poor. Increased prenatal investment did not trade off against maternal survival. In fact we found the opposite relationship: females with greater levels of prenatal investment had elevated postnatal maternal survival. Our results support the hypothesis that mammalian prenatal development is responsive to the intensity of postnatal competition. Understanding whether these responses are adaptive requires information on the long-term consequences of prenatal investment for offspring fitness.ER

Survival costs of reproduction predict age-dependent variation in maternal investment.

Life-history theory predicts that older females will increase reproductive effort through increased fecundity. Unless offspring survival is density dependent or female size constrains offspring size, theory does not predict variation in offspring size. However, empirical data suggest that females of differing age or condition produce offspring of different sizes. We used a dynamic state-variable model to determine when variable offspring sizes can be explained by an interaction between female age, female state and survival costs of reproduction. We found that when costs depend on fecundity, young females with surplus state increase offspring size and reduce number to minimize fitness penalties. When costs depend on total reproductive effort, only older females increase offspring size. Young females produce small offspring, because decreasing offspring size is less expensive than number, as fitness from offspring investment is nonlinear. Finally, allocation patterns are relatively stable when older females are better at acquiring food and are therefore in better condition. Our approach revealed an interaction between female state, age and survival costs, providing a novel explanation for observed variation in reproductive traits

Evolutionary analysis of life span, competition, and adaptive radiation, motivated by the Pacific rockfishes (Sebastes).

The Pacific rockfishes (Sebastes spp) are remarkable for both their diversity (on the order of 100 species) and range of maximum life span ( approximately 10 years for Calico rockfish to approximately 200 years for Rougheye rockfish). We describe the natural history and patterns of diversity and life span in these species and then use independent contrasts to explore correlates of these. When phylogenetic history is taken into account, maximum life span is explained by age at maturity, size at maturity, and the interaction of these two. We introduce a life-history model that allows insight into the origin of these correlations. We then describe a variety of mechanisms that may increase lifepans and diversity. These include fluctuating environments (in which organisms basically have to "wait out" bad periods to reproduce successfully), diversity, and longevity inspired by interspecific competition and physiological complexity in growth and accumulation of cellular damage. All of the results point toward the importance of flat or "indifferent" fitness surfaces as a key element in the evolution of diversity. We conclude that further development of the theory of flat or indifferent fitness surfaces as applied to diversity and life span is clearly warranted

Recent declines in salmon body size impact ecosystems and fisheries.

Declines in animal body sizes are widely reported and likely impact ecological interactions and ecosystem services. For harvested species subject to multiple stressors, limited understanding of the causes and consequences of size declines impedes prediction, prevention, and mitigation. We highlight widespread declines in Pacific salmon size based on 60 years of measurements from 12.5 million fish across Alaska, the last largely pristine North American salmon-producing region. Declines in salmon size, primarily resulting from shifting age structure, are associated with climate and competition at sea. Compared to salmon maturing before 1990, the reduced size of adult salmon after 2010 has potentially resulted in substantial losses to ecosystems and people; for Chinook salmon we estimated average per-fish reductions in egg production (-16%), nutrient transport (-28%), fisheries value (-21%), and meals for rural people (-26%). Downsizing of organisms is a global concern, and current trends may pose substantial risks for nature and people

Recent declines in salmon body size impact ecosystems and fisheries.

Declines in animal body sizes are widely reported and likely impact ecological interactions and ecosystem services. For harvested species subject to multiple stressors, limited understanding of the causes and consequences of size declines impedes prediction, prevention, and mitigation. We highlight widespread declines in Pacific salmon size based on 60 years of measurements from 12.5 million fish across Alaska, the last largely pristine North American salmon-producing region. Declines in salmon size, primarily resulting from shifting age structure, are associated with climate and competition at sea. Compared to salmon maturing before 1990, the reduced size of adult salmon after 2010 has potentially resulted in substantial losses to ecosystems and people; for Chinook salmon we estimated average per-fish reductions in egg production (-16%), nutrient transport (-28%), fisheries value (-21%), and meals for rural people (-26%). Downsizing of organisms is a global concern, and current trends may pose substantial risks for nature and people

Thresholds of coral cover that support coral reef biodiversity

Global environmental change, such as ocean warming and increased cyclone activity, is driving widespread and rapid declines in the abundance of key ecosystem engineers, reef-building corals, on the Great Barrier Reef. Our ability to understand how coral associated species, such as reef fishes, respond to coral loss can be impeded by uncertainty surrounding natural spatio-temporal variability of coral populations. To address this issue, we developed a semi-parametric hierarchical Bayesian model to estimate long-term trajectories of habitat-forming coral cover as a function of three spatial scales (sub-region, habitat and site) and environmental disturbances. The relationships between coral cover trajectories and fish community structure were examined using posterior predictive distributions of estimated coral cover from the statistical model. In the absence of direct observations of fish community structure, we used the probability of coral cover being above some ecological threshold values as a proxy for potential disruptions of fish community structure. Threshold values were derived from published field studies that estimated changes in the structure of coral-reef fish communities and coral cover after major disturbances. In these studies, fish community structure did not change where post-disturbance coral cover was &amp;gt; 20%. Disruptions in the structure of these communities were observed when coral cover dropped to between 10–20% and declines in fish diversity were typical where coral cover ranged from between 5 and 10%. Based on these thresholds values, posterior probabilities of coral cover being above 20% and between 10 and 20% and between 5 and 10% were calculated across spatial scales on the Great Barrier Reef (GBR) from 1995 to 2011. At the GBR scale, probabilities of coral cover being above these thresholds remained relatively stable through time. Across years, probabilities of coral cover being at least &amp;gt; 20% remained null for the sub-regions of Cairns, Townsville, Whitsundays and Swain but highly variable between reef sites within these sub-regions, with the exception of Townsville. In the Townsville area, probabilities of coral cover being between 10–20% and 5–10% declined from 0.75 to 0 during the study period. This finding highlights potential sub-regional fish community structure disruptions which have not yet been observed at this spatial scale. As frequency and intensity of disturbance events continue to rise, and consequently, as coral cover declines further, the probabilistic Bayesian approach presented in this chapter could be used to help provide early warnings of major ecological shifts at management relevant scales in the absence of direct observations.</p