Brown, C J

Brown, I. W.

Doubell, Mark

Lee, S. Y.

LEMCKERT, Charles

Redondo Rodriguez, Ana

SPENCER, David

Zhang, Hong

English

Catchability is a key parameter used for stock management of fisheries. Factors which influence catchability are largely associated with fishing methods and species abundance; however, oceanographic processes play an important role during different stages of many fisheries species’ lifecycles and, therefore, can also influence catch rates. For example, ambient temperature may affect the behaviour of crabs by influencing their energy and activity levels, which in turn affects their emergence patterns and availability to the fishery. Previous work suggest favourable catches of spanner crab can be attributed to stronger currents and warmer ambient temperatures, prompting the need to quantify processes responsible for current and temperature changes in the Bottom Boundary Layer (BBL) of the fishery. In the southern part of the Queensland spanner crab fishery, located on the east coast of Australia, sea surface temperature (SST) and alongshore wind stress was trialled as possible indicators of BBLT temperature (BBLT) and, consequently, catches of spanner crab. Using Generalised Linear Models (GLM), our findings display evidence that cooler BBLT and upwelling-favourable wind stress significantly improves daily spanner crab catch rates. This significant, inversely proportional trend between BBLT and catch rates opposes previous work and, thus, emphasises the importance of multiple hypotheses when relating oceanographic processes to the abundance, distribution, and availability of fisheries species. Future studies on BBLT affecting the catchability of spanner crabs would benefit from taking into consideration the variability of oceanographic processes across greater spatial scales (i.e. the whole fishery)

University of Canberra Research Repository

The effects of  wind stress and temperature on the catchability of  spanner crab (Ranina ranina) in South-East Queensland, AustraliaDavid M. Spencer*1,3, Ian W. Brown2, Mark J. Doubell3, Christopher J. Brown1, Ana Redondo-Rodriguez3, Shing Y. Lee4, Hong Zhang1, and Charles J. Lemckert51 Griffith University, Australia    2 Queensland Department of  Fisheries (ret’d), Australia    3 SARDI Aquatic Sciences, Australia    4 The Chinese University of  Hong Kong, China    5 University of  Canberra, AustraliaBACKGROUNDCatchability is an important parameter for stock assessmentmodelling and improving the economic efficiency ofcommercial fishing operations. Previous research found apositive relationship between bottom boundary layertemperature (BBLT) and catch rates of spanner crabs in theAustralian fishery1. Our aim was to understand how localoceanographic processes, specifically wind-drivenupwelling/downwelling, affected this relationship in South-East Queensland (SEQ), Australia.RESULTS▪SST a poor indication of BBLT and catch rates▪BBLT, τ7, and catch rates illustrated very similarseasonal cycles (Fig. 2)▪Catch rates spiked during seasonal BBLT cooling,more frequent northerlies, and annual matingaggregation (blue shaded area)▪Catch rates declined around the end of summer(orange shaded area) and were generally steadyduring autumn and winter▪BBLT and τ7 were significantly related and inverselyproportional to catch rates during autumn andwinter (Table 1)METHODOLOGY▪Metocean parameters BBLT, sea surface temperature (SST), andwind data were sourced from three monitoring platforms (Fig. 1)for years 2011-2014▪Corresponding catch rate data were estimated by standardizingtotal catch (kg) using total net lifts as a measure of effort for thestudy region (Fig. 1)▪Alongshore wind stress was calculated2 and low-pass filteredusing a 7-day running mean (τ7)▪Generalised Linear Models (GLM) were used to model the effectof using SST or τ7 in lieu of BBLT and to measure seasonalinteractions▪Each model and explanatory variable were assessed usingexplained deviance and confidence intervalsThe spanner crab (above) inhabits subtropical shelfwaters of the Indo-Pacific, caught using size- andspecies-selective tangle nets (below)*david.spencer2@griffithuni.edu.auGLM Season CI (2.5%) CI (97.5%) ED(%)BBLT+ offset(Net lifts)summer -.10 .0128autumn* -.15 -.03winter* -.15 -.05spring -.09 .03τ7+ offset(Net lifts)summer -3.37 5.0410autumn* -18.57 -9.78winter* -21-69 -12.6spring -4.37 6.53     03 05 07 09 11 01 03 05 07 09 11 01 03 05 07 09 11 01 03 05 07 09 11-0.1-0.0500.050.10.157 (Nm-2)|-----------------2011----------------||-----------------2012----------------||-----------------2013-----------------||-----------------2014-----------------| 03 05 07 09 11 01 03 05 07 09 11 01 03 05 07 09 11 01 03 05 07 09 11182022242628SST (o C)03 05 07 09 11 01 03 05 07 09 11 01 03 05 07 09 11 01 03 05 07 09 111618202224Month (mm)BBLT (o C)03 05 07 09 11 01 03 05 07 09 11 01 03 05 07 09 11 01 03 05 07 09 1100.511.5Standardised CatchMonth (mm)SUMMARY▪Our results oppose the previous study1, which wasconducted over a larger spatial scale▪Spanner crabs may be using upwelling as a cue forannual mating aggregation▪Off-season (autumn-winter) episodic BBLT cooling,occasionally attributed to wind-driven upwelling,can be useful in helping explain short-termfluctuations in catch ratesTable 1 – Seasonal effect of BBLT and τ7 on catch rates. CI: lower(2.5%) and upper (97.5%) confidence limits. ED(%): percentage ofexplained devianceFig. 1 – Study region inside Australian spanner crab (SC) fishery.BBLT data from NRSNSI mooring, SST from waverider buoy, andwind data from weather station. ‘Crabbing zone’ in 30-80 m* significant within the 95% CIFig. 2 –Daily SST, τ7, BBLT, and catch rate data from 2011-2014. Date ticks correspond with the middle ofthe labelled month (day 15). Positive and negative τ7 represents southerlies and northerlies, respectively. Blueshaded area highlight higher catch rates and seasonal upwelling. Orange shaded areas highlight the periodwhen catch rates start to decline and BBLT warming1. Brown IW et al. Ecological assessment - Queensland spanner crab fishery.Department of Primary Industries, Brisbane. 2001.2. Large WG, Pond S. Open ocean momentum flux measurements in moderateto strong winds. Journal of physical oceanography. 198150 mm

The effects of temperature and alongshore wind stress on the catchability of spanner crab (Ranina ranina)

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The effects of temperature and alongshore wind stress on the catchability of spanner crab (Ranina ranina)

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