Comparative demography of commercially important species of coral grouper, Plectropomus leopardus and P. laevis, from Australia's great barrier reef and Coral Sea marine parks

Abstract

Understanding the spatial and environmental variation in demographic processes of fisheries target species, such as coral grouper (Genus: Plectropomus), is important for establishing effective management and conservation strategies. Herein we compare the demography of Plectropomus leopardus and P. laevis between Australia's Great Barrier Reef Marine Park (GBRMP), which has been subject to sustained and extensive fishing pressure, and the oceanic atolls of Australia's Coral Sea Marine Park (CSMP), where there is very limited fishing for reef fishes. Coral grouper length-atage data from contemporary and historical otolith collections across 9.4 degrees of latitude showed little difference in lifetime growth between GBRMP and CSMP regions. Plectropomus laevis populations in GBRMP reefs had significantly higher rates of total mortality than populations in the CSMP. Mean maximum lengths and mean maximum ages of P. laevis were also smaller in the GBRMP than in the CSMP, even when considering populations sampled within GBRMP no-take marine reserves (NTMRs). Plectropomus leopardus, individuals were on average smaller on fished reefs than NTMRs in the GBRMP, but all other aspects of demography were broadly similar between regions despite the negligible levels of fishing pressure in the CSMP. Similarities between regions in growth profiles and length-at-age comparisons of P. laevis and P. leopardus suggest that the environmental differences between the CSMP and the GBRMP may not have significant impacts on lifetime growth. Our results show that fishing may have influenced the demography of coral grouper on the GBR, particularly for the slower growing and longer lived species, P. laevis. K E Y W O R D S coral grouper, Coral Sea, demography, great barrier reef, marine reserve, Plectropomus 1 | INTRODUCTION Coral reef fishes can show remarkable plasticity in their life history in response to anthropogenic pressures (e.g., fishing; Rochet, 1998) or environmental variation (e.g., temperature; Choat & Robertson, 2002; Mora, 2015; Taylor et al., 2019). Understanding the factors that influence demographic traits like lifetime growth and mortality are essential for developing population or species-specific management strategies,

Regional versus latitudinal variation in the life‐history traits and demographic rates of a reef fish, Centropyge bispinosa, in the Coral Sea and Great Barrier Reef Marine Parks, Australia

“…Therefore, it is possible that improved quality and/or quantity of dietary resources on GBRMP reefs may have resulted in greater mean maximum length of C. bispinosa populations compared to CSMP populations. It is notable that greater asymptotic or maximum length on GBRMP reefs of comparable latitude to those in the CSMP were not evident for the piscivores Plectropomus leopardus and P. laevis (Payet et al ., 2020), possibly due to differences in diet, behaviour or adaptive variation.…”

Demographic histories shape population genomics of the common coral grouper (Plectropomus leopardus)

“…We used a generation time ( t2 ) of 8.25 years based on the formula by Pianka (1978): t2 = ( a + w )/2, where a = mean age (years) at 50% maturity and w = longevity (years). We set a at 2.5 years and w at 14 years based on the known life history of P. leopardus in the GBR (Adams et al, 2000; Ferreira & Russ, 1994; Russ et al, 1998) and the Coral Sea (Payet et al, 2020).…”

“…In contrast, the Australian Coral Sea Marine Park (herein referred to as the Coral Sea), which borders the GBR to the east, and contains 37 coral reef atolls, has provided a comparatively stable habitat over similar evolutionary time scales as the region is characterized by a deep oceanic basin that prevented complete exposure during lower sea level stands (Figure 1 ). Reefs in the Coral Sea also occupy unique temperature regimes (Payet et al, 2020 ) and are surrounded by well‐mixed, oligotrophic waters that are far removed from the coastal rainfall, nutrient and sediment runoff that influence the marine environment in the GBR.…”

“…In the Coral Sea, P. leopardus is found on several isolated atoll reefs, and while these populations are relatively unfished at present (Payet et al, 2020), the extent of connectivity with the GBR and the relative reliance on self‐recruitment is not known. Cross‐shelf patterns of the genetic structure are also rarely considered in fisheries management, despite an increasing number of studies identifying distinct inshore and offshore ecotypes in marine organisms (e.g., Atlantic cod; Barth et al, 2017, European anchovy; Bonhomme et al, 2022, Gulf pipefish; Flanagan et al, 2021, seahorses; Riquet et al, 2019, and dolphins; Louis et al, 2021).…”

Minimum size limits and the reproductive value of numerous, young, mature female fish

“…BOFFFFs have the potential to make a disproportionate contribution to population replenishment by generating more, and potentially higher quality offspring [30,31]. However, commercial and recreational fisheries often target larger fish, reducing the density of BOFFFFs and size at maturation, resulting in the truncation of a population's age and size distribution [32][33][34], all of which ultimately leads to declining larval supply and stock productivity. Despite high fecundity, the scarcity of larger individuals suggests their overall contribution to population replenishment could be low.…”