Combining catch-based indicators suggests overexploitation and poor status of Indonesia's deep demersal fish stocks

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The Indonesian deep-slope demersal fisheries are economically valuable and contribute to the wellbeing of millions of people. However, the sustainability of these fisheries is uncertain because they lack data and assessment. As a precursor to management, we developed and applied a framework for using standardized catch per unit effort (CPUE) and spawning potential ratio (SPR) as indicators to assess eight primary species-fishing gear complexes: the Malabar blood snapper Lutjanus malabaricus (droplines and longlines), goldbanded jobfish Pristipomoides multidens (droplines and longlines), sharptooth jobfish P. typus (droplines and longlines), crimson snapper L. erythropterus (droplines), and rusty jobfish Aphareus rutilans (droplines). We standardized CPUE by identifying relevant fishing trips using a species-association approach and removing any changes in the index not attributable to abundance by using a delta-generalized linear model. SPR values were estimated on a per-recruit basis from life-history parameters using length data. Results indicated that in 2020, all stocks were unhealthy (SPR values < 25%) with only a few exceptions (e.g., P. multidens and L. erythropterus). Most fishing grounds with low SPR values had stable or decreasing CPUE trends, suggesting that current fishing rates are suboptimal or unsustainable. However, L. erythropterus had an increasing CPUE trend but moderate to low SPR, indicating that fishing pressure has decreased so SPR may be an underestimate, leading to an optimistic but uncertain conclusion about stock health and the sustainability of current fishing rates. Such discrepancies between CPUE and SPR may be challenging for the implementation of management measures, but we have outlined and applied a framework for interpretation. The most recent yield values set by the Indonesian Ministry of Marine Affairs and Fisheries for these stocks, however, are 1.4–2.4 times higher than our calculations. This discrepancy may be attributed to several factors, such as inclusion of species that are atypical for deep demersal fish stocks in the Ministry's estimates, differences in methods or the types of data used, or annual variability.

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Fisheries Research