Changing growth pattern in small pelagic species targets of purse seine fisheries in Southwestern Atlantic
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1
Federal University of Paraná, Brazil
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2
Interdisciplinary Center for Marine and Environmental Research, Abel Salazar Institute of Biomedical Sciences, University of Porto, Portugal
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3
Universidade do Vale do Itajaí, Brazil
Purse seine fleet in the Southwestern Atlantic sustains the most important fishery of Brazil, whose target is Sardinella brasiliensis and other important species, highlighting Opisthonema oglinum and Chloroscombrus chrysurus. This fishing fleet operates at the continental shelf between 22oS-28o36’S, sometimes up to 30oS. Last official statistics concerning landings (2011) presents values of 75,122.5 tons for S. brasiliensis, 8,810.3 tons for O. oglinum and 2,832.8 tons for C. chrysurus. Historical landings (1997-2018) evidenced that inter annual variability of S. brasiliensis catches led to an increase importance of these other species in the landings, detected in regional monitoring programs. Although not continuous in time, biological samplings on landings were taken, providing a robust database to evaluate important biological aspects of these species, among them growth patterns, a key issue for ecological and fisheries assessments. For an initial and rapid diagnostic, modal progression analysis were apply for total length data (TL, mm) of O. oglinum and C. chrysurus. After tests and looking for numerical sufficiency, data were monthly grouped in quadrenniums for O. oglinum (1997-2018, excluding 2014) and three groups for C. chrysurus (2006-2008, 2009-2011 and 2012-2018). Growth parameters were estimate for each period by using the software FiSAT II, routine ELEFAN I (K-Scan method) based on 15 mm TL size classes. Restructured frequencies were analyzed to check von Bertalanffy growth curves accuracy. O. oglinum (range of 122-395 mm TL, n = 5,927) shown opposite trends in relation to S. brasiliensis catches, increasing when S. brasiliensis decreased and vice versa. The same has occurred with C. chrysurus (range of 147-400 mm TL, n = 2,271), just in a small scale. Size structure reflected fishing gear selectivity, avoiding juvenile catches (< 15 mm TL). Growth patterns of the two species responded to different fishing pressure along the time. In 1997-2000, the collapse of S. brasiliensis lead to an increase of O. oglinum catches, which presented longer sizes and older fishes, reflecting in the highest L∞ value (L∞ = 417.38 mm and K = 0.77/yr). In the following period (2001-2004), S. brasiliensis catches increased again, reducing O. oglinum catches. Growth parameters responded to the fishing pressure of the previous period, with a reduction in the size/age (L∞ = 307.13 mm, k = 1.10/year), a probable consequence of the intraspecific competition reduction. In the two next periods (2006-2009 and 2010-2013), O. oglinum apparently recovered, presenting another increase in its landings followed by a decrease. Growth parameters tended to reflect this and stabilize in these two periods (L∞ = 370.13 mm, K = 0.74/year and L∞ = 370.13 mm – the same, K = 0.87/year). In the forthcoming period (2015-2018), catches of O. oglinum increased, but it seems that the stock did not recover, with the lowest size/age structure (L∞ = 322.88 mm and K = 0.59/yr). Growth parameters of C. chrysurus also reflected variations in its catches, with a clear tendency of size/age reduction along the time. Since 1997, the highest catches of the specie occurred during 2006-2008, with highest growth rate (K = 1.00/yr and L∞ = 385.88 mm). In 2009-2011 its catches declined, with an apparent recovery (L∞ = 417.38 mm, K = 0.48/yr). In the last period (2012-2018), C. chrysurus catches reduced, with a peak only in 2017 when S. brasilliensis catches decreased again. Growth parameters reduced to 385.88 mm and 0.39/yr. Although preliminary, the current assessment indicated a scenario of changing growth parameters due to changes in size and age structure of O. oglinum and C. chrysurus, probably related to purse seine fleet operations in the Southwestern Atlantic. Growth parameters were coherent with the exploitation in the periods analyzed, even under different environmental conditions throughout the time. Namely, fishing after periods of little catches tend to exhibit larger and older individuals, reflecting in higher values of L∞ and smaller K values. A reduction in both growth parameters deserves attention, what happened in both species in the last periods analyzed, probably due to overfishing. Previous estimates of growth parameters in the same area for O. oglinum (L∞ = 216.4 mm, K = 0.35/yr) and C. chrysurus (L∞ = 451 mm, K = 0.22/yr) date back to 1997-1998, based on macrostructural otolith analysis. They were remarkable different for O. oglinum, after detected as a fast growth species (otolith microincrements analysis), which support the current estimates. For C. chrysurus, the differences observed deserve further investigations. Macro and microstructural otolith analyses already initiated for both species will refine the current results that, even preliminary, are robust enough to give support to the management of these species.
Acknowledgements
FUNBIO TAC Chevron for KAR scholarship. CNPq Research grant for AMVS (310451/2018-3).
Keywords:
Opisthonema oglinum,
Chloroscombrus chrysurus,
Modal progression analysis,
time series,
Brazil
Conference:
XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019.
Presentation Type:
Poster
Topic:
ECOLOGY AND LIFE CYCLES
Citation:
Rautenberg
KA,
Correia
AT,
Schwingel
PR and
Vaz-dos-Santos
AM
(2019). Changing growth pattern in small pelagic species targets of purse seine fisheries in Southwestern Atlantic.
Front. Mar. Sci.
Conference Abstract:
XVI European Congress of Ichthyology.
doi: 10.3389/conf.fmars.2019.07.00021
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Received:
30 May 2019;
Published Online:
14 Aug 2019.
*
Correspondence:
Dr. André M Vaz-dos-Santos, Federal University of Paraná, Curitiba, Paraná, 80060-000, Brazil, andrevaz@gmail.com