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Growth, maturity, and length-based spawning potential of tusk in the Norwegian and Barents Seas
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DOI：10.1093/icesjms/fsag113.png)
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Abstract
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Slow-growing, late-maturing deep-sea fish are vulnerable to overfishing and climate change. Tusk (Brosme brosme), an important North Atlantic species, remains understudied across much of its range, limiting fishing advice. We analyzed growth, age, reproduction, and mortality of tusk in the Norwegian and Barents Seas using survey and commercial data from the Norwegian Institute of Marine Research (2000–2022). These analyses provide updated life history parameters essential for stock assessment and management. Using these parameters, we applied the LBSPR model to estimate annual SPR. We also implemented a stochastic version of LBSPR, parameterized with general tusk-like traits, to evaluate how uncertainty in key biological inputs affects SPR estimates when stock-specific parameters are unavailable. This allowed us to evaluate LBSPR as a data-limited, length-based diagnostic, assess how well it aligns with the existing stock assessment framework, and consider its potential applicability to tusk stocks in other regions. Tusk with estimated longevity of 22 years in the Norwegian and Barents Seas appear longer-lived and mature at larger sizes than populations in the Northwest Atlantic. Von Bertalanffy growth parameters varied between sexes, with asymptotic length (Linf) of 74.4–77.6 cm, growth coefficient (K) 0.11–0.12 year⁻¹, and theoretical age at zero length (t₀) − 0.42- −0.52 years. Length at 50% maturity (L₅₀) ranged from 48.3 to 58.1 cm, and age at maturity (A₅₀) for males and females was 10.2 and 11.7 years, respectively. Spawning likely occurs from late spring to early summer. Mean stochastic SPR estimates remained high (>41%) in 2001–2022, despite substantial uncertainty. Stock-specific SPR estimates consistently exceeded simulated 95% MSY reference points, and most annual values were above commonly used management targets (SPR > 0.3–0.4). This study fills key knowledge gaps in tusk biology, reveals regional demographic variation, and demonstrates the utility of stock-specific LBSPR for data-limited fisheries. While stochastic LBSPR may be informative when stock-specific data is unavailable, its high uncertainty indicates a need for further refinement. The life history parameters and length-composition summaries developed here are intended as auxiliary inputs to priors on productivity, natural mortality, selectivity, and maturity for upcoming benchmark assessments and future management strategy evaluation work.
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