Fish otoliths' chronometric properties make them useful for age and growth rate estimation in fisheries management. For the Eastern Baltic Sea cod stock (
- Award ID(s):
- 1923965
- NSF-PAR ID:
- 10455793
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Fish Biology
- Volume:
- 97
- Issue:
- 2
- ISSN:
- 0022-1112
- Page Range / eLocation ID:
- p. 552-565
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Accurate age data are essential for reliable fish stock assessment. Yet many stocks suffer from inconsistencies in age interpretation. A new approach to obtain age makes use of the chemical composition of otoliths. This study validates the periodicity of recurrent patterns in 25 Mg, 31 P, 34 K, 55 Mn, 63 Cu, 64 Zn, 66 Zn, 85 Rb, 88 Sr, 138 Ba, and 208 Pb in Baltic cod (Gadus morhua) otoliths from tag–recapture and known-age samples. Otolith P concentrations showed the highest consistency in seasonality over the years, with minima co-occurring with otolith winter zones in the known-age otoliths and in late winter – early spring when water temperatures are coldest in tagged cod . The timing of minima differs between stocks, occurring around February in western Baltic cod and 1 month later in eastern Baltic cod; seasonal maxima are also stock-specific, occurring in August and October, respectively. The amplitude in P is larger in faster-growing western compared with eastern Baltic cod. Seasonal patterns with minima in winter – late spring were also evident in Mg and Mn, but less consistent over time and fish size than P. Chronological patterns in P, and to a lesser extent Mg and Mn, may have the potential to supplement traditional age estimation or to guide the visual identification of translucent and opaque otolith patterns used in traditional age estimation.more » « less
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Deoxygenation worldwide is increasing in aquatic systems with implications for organisms' biology, communities and ecosystems. Eastern Baltic cod has experienced a strong decline in mean body condition (i.e. weight at a specific length) over the past 20 years with effects on the fishery relying on this resource. The decrease in cod condition has been tentatively linked in the literature to increased hypoxic areas potentially affecting habitat range, but also to benthic prey and/or cod physiology directly. To date, no studies have been performed to test these mechanisms. Using otolith trace element microchemistry and hypoxia-responding metrics based on manganese (Mn) and magnesium (Mg), we investigated the relationship between fish body condition at capture and exposure to hypoxia. Cod individuals collected after 2000 with low body condition had a higher level of Mn/Mg in the last year of life, indicating higher exposure to hypoxic waters than cod with high body condition. Moreover, lifetime exposure to hypoxia was even more strongly correlated to body condition, suggesting that condition may reflect long-term hypoxia status. These results were irrespective of fish age or sex. This implies that as Baltic cod visit poor-oxygen waters, perhaps searching for benthic food, they compromise their own performance. This study specifically sheds light on the mechanisms leading to the low condition of cod and generally points to the impact of deoxygenation on ecosystems and fisheries.more » « less
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Abstract Chemical analysis of calcified structures continues to flourish, as analytical and technological advances enable researchers to tap into trace elements and isotopes taken up in otoliths and other archival tissues at ever greater resolution. Increasingly, these tracers are applied to refine age estimation and interpretation, and to chronicle responses to environmental stressors, linking these to ecological, physiological, and life-history processes. Here, we review emerging approaches and innovative research directions in otolith chemistry, as well as in the chemistry of other archival tissues, outlining their value for fisheries and ecosystem-based management, turning the spotlight on areas where such biomarkers can support decision making. We summarise recent milestones and the challenges that lie ahead to using otoliths and archival tissues as biomarkers, grouped into seven, rapidly expanding and application-oriented research areas that apply chemical analysis in a variety of contexts, namely: (1) supporting fish age estimation; (2) evaluating environmental stress, ecophysiology and individual performance; (3) confirming seafood provenance; (4) resolving connectivity and movement pathways; (5) characterising food webs and trophic interactions; (6) reconstructing reproductive life histories; and (7) tracing stock enhancement efforts. Emerging research directions that apply hard part chemistry to combat seafood fraud, quantify past food webs, as well as to reconcile growth, movement, thermal, metabolic, stress and reproductive life-histories provide opportunities to examine how harvesting and global change impact fish health and fisheries productivity. Ultimately, improved appreciation of the many practical benefits of archival tissue chemistry to fisheries and ecosystem-based management will support their increased implementation into routine monitoring.
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null (Ed.)Abstract. During the past 20 years, hypoxic areas have expanded rapidly in theBaltic Sea, which has become one of the largest marine “dead zones” in theworld. At the same time, the most important commercial fish population ofthe region, the eastern Baltic cod, has experienced a drastic reduction inmean body condition, but the processes behind the relation betweendeoxygenation and condition remain elusive. Here we use extensive long-termmonitoring data on cod biology and distribution as well as on hydrologicalvariations to investigate the processes that relate deoxygenation and codcondition during the autumn season. Our results show that the depthdistribution of cod has increased during the past 4 decades at the sametime of the expansion, and shallowing, of waters with oxygen concentrationsdetrimental to cod performance. This has resulted in a progressivelyincreasing spatial overlap between the cod population and low-oxygenatedwaters after the mid-1990s. This spatial overlap and the actual oxygenconcentration experienced by cod therein statistically explained a largeproportion of the changes in cod condition over the years. These resultscomplement previous analyses on fish otolith microchemistry that alsorevealed that since the mid-1990s, cod individuals with low condition wereexposed to low-oxygen waters during their life. This study helps to shedlight on the processes that have led to a decline of the eastern Baltic codbody condition, which can aid the management of this population currently indistress. Further studies should focus on understanding why the codpopulation has moved to deeper waters in autumn and on analyzing the overlapwith low-oxygen waters in other seasons to quantify the potential effects ofthe variations in physical properties on cod biology throughout the year.more » « less
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