A Decade of Monitoring an Indo-Pacific Grouper Spawning Aggregation: Benefits of Protection and Importance of Survey Design

Abstract

Groupers (Family Epinephelidae) are valuable and vulnerable reef-associated fishes. Medium to large-sized Indo-Pacific genera, such as Epinephelus and Plectropomus, are important in local/international trade, and are particularly susceptible to overfishing due to their economic value, longevity, late maturation and, for some species, aggregationspawning. Three species, Plectropomus areolatus, Epinephelus polyphekadion, Epinephelus fuscoguttatus, are threatened (IUCN Red List) and, when exploited on their aggregations, typically undergo declines unless managed. To effectively assess spawning aggregation status and identify changes over time following fishing or management, a robust sampling protocol is essential. This was developed and tested at a protected, but previously depleted, spawning site shared by these three species in Palau, western Pacific. Underwater visual census (UVC) tracked changes in fish abundance (numbers) across their aggregation site between 2009 and 2019. Census data on abundance and density were complemented by additional technologies to generate a more complete picture of this aggregation site and the three species, including stationary cameras to monitor fish with divers absent, stereo-video to measure fish lengths, and oceanographic instruments to measure variability in currents and water temperature. Results show that protection outcomes depend on biology and on active enforcement and that UVC survey design must adequately address temporal/spatial variability to effectively document changes in fish abundance. Over the decade-long study, P. areolatus, the fastest-maturing species, showed a near fourfold increase in peak annual abundance (increasing from annual peak numbers of c.450 to 1,800 fish), followed by a more modest increase in E. polyphekadion (increase from c.500 to at least 600 fish and a twofold density increase) and relative stability in the slowest maturing, longest-lived species, E. fuscoguttatus (stable between approximately 300 and 450 fish). The study highlighted need for caution when fish density is used as a proxy for

Stock Performance and Fishers’ Perception of Grouper and Snapper Fisheries in the Saleh Bay, Indonesia

“…Regarding the ecological dimension, it is observed that the CPUE trend, stock status, and changes in the size of the fish caught promote ecological sustainability. A combination of a closed fishing season and a closed area, especially in fish spawning aggregation sites, is recommended to complement conventional fishery management measures [3], [48], mainly to protect juveniles.…”

Standard histological techniques systematically under‐estimate the size fish start spawning

“…While spawning was not observed for the other species, which we presume spawn at night (e.g. Sadovy de Mitcheson et al, 2020), the definition of spawning aggregations proposed by Domeier and Colin (1997) was fulfilled. For all species other than C. striatus , we sampled aggregations on at least two different days, and for some species at multiple aggregation sites around Palau (Table S1).…”

“…While spawning was not observed for the other species, which we presume spawn at night (e.g. Sadovy de Mitcheson et al, 2020), the definition of spawning aggregations proposed by Domeier and Colin (1997) was fulfilled.…”

“…Palau has a well‐documented body of fisher knowledge about the location and timing of spawning aggregations (Sadovy de Mitcheson et al, 2020; Sakaue et al, 2016). On the basis of having known and accessible spawning times and locations we selected for study ten species from six common tropical families (Table 1).…”

Scientometric analysis and literature synthesis of 60 years of science on the Atlantic goliath grouper (Epinephelus itajara)

“…The species most sensitive to the risk of extinction by fishing are those with large‐sized, slow‐growing and late‐maturing individuals (Denney et al ., 2002; Sadovy, 2001; Tsoukali et al ., 2016). These species are highly valued in the market (due to the quality of the meat) and usually have limited geographical range and sporadic recruitment, such as many grouper species (Chiappone et al ., 2000; Sadovy, 1994; Sadovy, 2001; Sadovy De Mitcheson et al ., 2020; Sáenz‐Arroyo et al ., 2005).…”