No abstract

The consistent supply of fresh fish to commercial markets may mask growing fishing footprints and localized depletions, as fishing expands to deeper/further reefs, smaller fish, and more resilient species. To test this hypothesis, species-based records and fisher interviews were gathered over one year within a large, demand-driven coral-reef fishery in Chuuk, Micronesia. We first assessed catch statistics with respect to high windspeeds and moon phases that are known to constrain both catch and effort. While lower daily catch success was predicted by higher windspeeds and greater lunar illumination, total daily landings fluctuated less than fishing success across environmental gradients. Instead, daily landings were mainly driven by the number of flights from Chuuk to Guam (i.e., international demand). Given that demand masked local drivers of overall catch volume, we further evaluated species-based indicators of fisheries exploitation. Most target species (75%) had either a positively skewed size distribution or proportional contributions that were dependent upon favorable conditions (i.e. season and moon phases). Skewed size distributions indicated truncated growth associated with fishing mortality, and in turn, suggested that size-based management policies may be most effective for these species. In contrast, environmentally-constrained catch success indicated species that may be more susceptible to growing fishing footprints and may respond better to gear/quota/area policies compared to size policies. Species-based responses offered a simplified means to combine species into fisheries management units. Finally, a comparison of commercial and subsistence landings showed higher vulnerability to fishing among species preferentially targeted by commercial fisheries, offering new insights into how commercial harvesting can disproportionately impact resources, despite having lower annual catch volumes.

Highfin grouper Epinephelus maculatus sampled in Chuuk, Micronesia, exhibited a moderate growth rate and a relatively short life span compared to other epinephelids of a similar size. Combined gonad and otolith analysis provide preliminary evidence that the species conforms to a protogynous sexual pattern. Mean total length at maturity for females was 308 mm with first age at maturity 2·8 years for females and 4 years for males, which differs from other regional studies. Based on the gonado-somatic index and microscopic analysis of gonads, E. maculatus in Chuuk have a 4 month spawning season (January to April) that corresponds with seasonal lows in sea surface water temperature and overlaps with that of other aggregating epinephelids. The estimated von Bertalanffy growth factor (K) was 0·51 year(-1) , while total mortality was 0·34 year(-1) . Current management for E. maculatus in Chuuk includes a January to May catch, sale and export ban, which overlaps with its reproductive season. The effectiveness of these arrangements will require on-going monitoring to determine whether alternative management strategies are required to ensure population persistence.

Spatial expansions can provide a false sense of sustainability to fish markets and their consumers who perceive stable landings through time despite localized depletions. This study examined attributes of monthly landings and changes in size structures within a commercial coral-reef fishery that had stable landings for 11 years. Regression models revealed a significant rise in the ratio of landings between calm and windy months, depicting that stable landings were driven by increased fishing effort or success during the calmer months when less exploited reefs became accessible. Within the calmer months, ''race-to-fish'' dynamics also evolved for some target species, such as parrotfishes, whose landings became increasingly concentrated towards the onset of calm favorable conditions. During this same time, the size structure for 15 out of 19 target species that comprised 60% of annual landings decreased. The cumulative results suggested that (1) spatial management units can be improved by taking environmental gradients that define fishing access into consideration, and (2) thresholds for size-and-agebased policies should be established with respect to life-history parameters that maximize cohort production and protect against declining size structures. Both recommendations resonate with traditional forms of management across the Pacific that were based on reef tenure and knowledge of how species respond to fishing pressure.

Summary Length–weight relationships (LWR) were estimated for six reef species in Chuuk lagoon (Federated States of Micronesia) captured by commercial fishers. Specimens were sampled opportunistically over a period of 2 months between July and September 2014. Relationships include those for four common species not currently reported in FishBase (Caesio teres, Myripristis adusta, Lethrinus erythracanthus, and Chlorurus frontalis), and for two species with relationships based on just one or two samples (Scarus oviceps, and Plectropomus oligacanthus). While estimates for some species are tentative given limited size‐range sampling, they still present an improvement in the currently available LWRs.

Between February 2015 and 2016, samples of the Indo-Pacific goldspotted spinefoot Siganus punctatus were taken from local fish markets, feeding sites and nursery grounds on the main island of Pohnpei, Micronesia, to ascertain sexual pattern, reproductive seasonality, age, growth and mortality. Microscopic examinations of gonads identified two seasonal peaks in reproduction: February to May and September to December, with evidence of some spawning activity in most months. Ripe females were observed 4 days on either side of the new moon. Females first matured at c. 180 mm fork length (L ) and 1 year of age, which coincides with their entry into the fishery. Ninety five per cent of individuals were less than 3 years and the oldest fish were 8 years. To examine the species vulnerability to fishing, a tag-and-recapture study was conducted over 4 months in 2015 in a locally managed marine area and at an unprotected site. Findings suggest high residency and high vulnerability to fishing at shallow-water feeding sites and restricted migration overall. The placement of marine protected areas within critical habitat appears to be an effective conservation strategy for this species, particularly when combined with gear and seasonal market restrictions during vulnerable life-history phases.

Population models are based upon the ideology that removing large, old individuals provides space for young, fast-growing counterparts that can maximize (fisheries) yields while maintaining population and ecosystem stability. Yet, we revealed that compensatory density dependence only existed for 49% of target coral-reef fishes exposed to growing fishing pressure across Pacific islands. Remaining species slowly disappeared from landings and reefs with limited population replenishment. To understand these remarkable differences, we constructed phylogenies for dominant fish families and discovered that large patristic distances between sister species, or greater isolation, predicted size-and-age truncation. Isolated species appeared to have greater niche dominance or breadth, supported by their faster growth rates and group foraging behavior. In contrast, closely related species may have more restricted, realized niches that led to their disappearance and replacement. Phylogenetic attributes offered novel guidance to proactively manage multispecies fisheries and improve our understanding of ecological niches and ecosystem stability.

Harvesting models are based upon the ideology that removing large, old individuals provides space for young, fast‐growing counterparts that can maximize (fisheries) yields while maintaining population stability and ecosystem function. Yet, this compensatory density dependent response has rarely been examined in multispecies systems. We combined extensive data sets from coral‐reef fisheries across a suite of Pacific islands and provided unique context to the universal assumptions of compensatory density dependence. We reported that size‐and‐age truncation only existed for 49% of target coral‐reef fishes exposed to growing fishing pressure across a suite of Pacific islands. In contrast, most of the remaining species slowly disappeared from landings and reefs with limited change to their size structure (i.e., little to no compensation), often becoming replaced by smaller‐bodied sister species. To understand these remarkable and disparate differences, we constructed phylogenies for dominant fish families and discovered that large patristic distances between sister species, or greater phylogenetic isolation, predicted size‐and‐age truncation. Isolated species appeared to have greater niche dominance or breadth, supported by their faster growth rates compared to species with similar sizes and within similar guilds, and many also have group foraging behavior. In contrast, closely related species may have more restricted, realized niches that led to their disappearance and replacement. We conclude that phylogenetic attributes offered novel guidance to proactively manage multispecies fisheries and improve our understanding of ecological niches and ecosystem stability.