Oceanic, Latitudinal, and Sex-Specific Variation in Demography of a Tropical Deepwater Snapper across the Indo-Pacific Region

Abstract

Deepwater tropical fisheries provide an important source of income and protein to Pacific and Indian Ocean coastal communities who are highly dependent on fish for food security. The development of quantitative assessments and management strategies for these deepwater fisheries has been hindered by insufficient biological and fisheries data. We examine the age-specific demography of the pygmy ruby snapper Etelis carbunculus, an important target species in tropical deepwater fisheries, across 90 • of longitude and 20 • of latitude in the Pacific and Indian Oceans. Our results show that growth of E. carbunculus varies significantly between oceans and sexes and across latitudes in both oceans. Estimates of natural and fishing mortality were similar between oceans, but higher for females than males in both oceans. Evidence of greater fishing pressure on females than males is likely due to the larger size-at-age of females compared to males, assuming that selectivity of the fishing gear is related directly to fish size. Sex ratios were significantly female biased in both oceans despite this species being gonochoristic, and maturity schedules were similar between sexes in the Pacific Ocean. This species exhibits a protracted spawning season from mid-spring to autumn (i.e., October to May) in the Pacific Ocean. These results represent the first estimates of age-specific demographic parameters for E. carbunculus, and provide the foundation for the development of the first species-specific assessment models and harvest strategies for the species. Future stock assessment models for E. carbunculus should consider sex-specific demographic parameters and spatial variation in demography. Our results reveal substantial differences in biology between E. carbunculus and the giant ruby snapper E. sp., a cryptic congeneric species, and thus contribute to greater clarity in managing fisheries that are dependent on these two species. Furthermore, the improved information on the life history of E. carbunculus contributes to the broader sustainable management and improved food security for deepwater snapper fisheries in the Indo-Pacific region.

Age‐based life history of humpback red snapper, Lutjanus gibbus, in New Caledonia

“…Williams et al . () provided a similar hypothesis to explain higher growth rates of female Etelis carbunculus Cuvier 1828, a deepwater lutjanid. Patterns of sexual dimorphism, such as that observed for L. gibbus , can complicate assessments of population status, especially in cases where the primary data source is abundance and length frequencies from fishery‐dependent or independent surveys (Taylor et al ., ).…”

“…The extended longevity observed for L. gibbus in southern New Caledonia relative to that reported for the species elsewhere is likely a function of environmental influences (including water temperature, food availability and competition), fishing pressure, genetics, or, most probably, a combination of factors (Conover et al ., ). The ability of individuals to reach greater longevity and larger body sizes at higher latitudes, where water temperature are generally cooler, has been documented in a number of shallow and deep‐water fish species with distributions spanning broad latitudinal and temperature ranges (Andrews et al ., ; Berumen et al ., ; Robertson et al ., ; Trip et al ., ; Williams et al ., ). At c .…”

“…Errors in estimates of M can have significant management implications. Gulland () and Deriso () recommend setting F at a value approximately equal to M ( i.e ., an exploitation rate E = 1.0) and a number of authors have since advocated this, or more conservative ratios ( e.g ., E = 0.5), as a reference point in catch‐curve analyses for data‐poor reef‐associated fisheries (Newman & Dunk, ; Rochet & Trenkel, ; Williams et al ., ). Under this management strategy ( i.e ., F ≈ M ), the use of an over‐inflated rate of M for populations in southern New Caledonia, resulting from an underestimation of maximum age (such as by using the maximum age estimate from American Samoa), would then allow F to be set too high, potentially leading to recruitment overfishing ( sensu Newman et al ., ).…”

“…The effect of sex on the L F – W T relationship was examined using generalised linear mixed‐effects models (GLMM), following the approach of Williams et al . (). Length and mass data were log‐transformed to satisfy the assumption of linearity.…”

Effects of exploitation evident in age-based demography of 2 deepwater snappers, the goldeneye jobfish (Pristipomoides flavipinnis) in the Samoa Archipelago and the goldflag jobfish (P. auricilla) in the Mariana Archipelago

“…Many Indo-Pacific fisheries that target tropical and subtropical deepwater snappers (Lutjanidae) are considered data poor with limited fisheries information and few reliable, detailed life history studies (Williams et al, 2012(Williams et al, , 2013Newman et al, 2015). The available information indicates that Pristipomoides species have long life spans (>30 years), slow to moderate growth rates, and low levels of natural mortality (Newman et al 1 ;Newman and Dunk, 2003;Andrews et al, 2012).…”