Elsevier

Fisheries Research

Volume 137, January 2013, Pages 63-70
Fisheries Research

Damage and physiological stress to juvenile eastern rock lobster (Sagmariasus verreauxi) discarded after trapping and hand collection

https://doi.org/10.1016/j.fishres.2012.09.001Get rights and content

Abstract

Large numbers of Sagmariasus verreauxi are trapped and hand collected in Australia, but discarded due to size and quota restrictions, and under the unevaluated assumption of few impacts. To test the validity of enforced discarding, trapped and hand-collected S. verreauxi (49–143 mm carapace length – CL) were examined for external damage, placed into cages, transferred to aquaria and monitored (with controls) over three months. Haemolymph was non-repetitively sampled immediately and at one, three, and seven days to quantify stress. Most trapped (64%) and hand-collected (79%) specimens were undersized (<104 mm CL), with the latter method yielding broader ranges of sizes and moult stages. Within-trap Octopus tetricus predation caused the only mortalities (3.3%). Hand collection resulted in much greater antennae and pereopod loss than trapping (53 vs. 4%) but, compared to controls, both methods evoked benign physiological responses that resolved within a week. While most wounded S. verreauxi regenerated all or some missing appendages post-moult, their mean CLs were less than those from intact conspecifics. Simple strategies, including larger mesh sizes, and/or installing modifications to reduce bycatch in traps, careful hand collection, and appropriate release techniques might minimise impacts (including predation) to unwanted S. verreauxi, and help to control stock exploitation.

Introduction

In Australia, the eastern rock lobster (Sagmariasus verreauxi; previously Jasus verreauxi) is distributed across coastal reefs (<∼200 m depth) south from Tweed Heads, New South Wales (NSW) to Port MacDonnell, South Australia (Montgomery, 1992, Kailola et al., 1993). The largest of all palinurids, S. verreauxi can attain substantial carapace lengths (>260 mm CL) and weights (>8 kg; Kailola et al., 1993), and is considered an iconic, highly prized species, particularly in NSW where it supports important commercial (∼130 metric tonnes; valued at $AUD 7.8 million annually; G. Liggins, pers. com.) and recreational fisheries (∼26 metric tonnes; Andrew et al., 1997).

A substantial proportion of the NSW S. verreauxi catch is taken from <10 m (hereafter referred to as shallow water) where, owing to positive age segregation by depth, there are large abundances of sublegal (<104 mm CL) juveniles (Montgomery, 1992). Shallow-water S. verreauxi are targeted with rectangular and round traps (Fig. 1), that are regulated by legal dimensions for both commercial and recreational fishers (≤1.2 m ø or 1.2 m × 1.2 m × 1.2 m), and numbers for the latter (one trap per fisher). Although not restricted, commercial fishers typically use 20–140 traps per licence. Mesh size is not regulated for recreational gears, but most rectangular traps are made from either 50 mm × 50 mm or 75 mm × 50 mm welded wire mesh, while round traps generally have ribs with 35–40 mm spaces (Fig. 1a and b). The minimum mesh size for commercial traps is 50 mm and there are plans to mandate “escape vents” in all traps, like those used in other crustacean trap fisheries (Murphy and Kruse, 1995, Arana et al., 2011), pending formal data on size and species selectivities.

In addition to trapping, both sectors can hand collect S. verreauxi while free diving (breath hold only), although this is almost entirely limited to recreational fishers. There are no definitive data on the proportion of the NSW recreational S. verreauxi catch taken by hand, but Henry and Lyle (2003) estimated that this method accounted for 32% of the national palinurid catch.

Along with gear regulations and minimum and maximum legal sizes (104 and 180 mm CL), NSW S. verreauxi are managed by quotas (annual catch for the commercial sector, typically 100–135 metric tonnes, or two individuals per day per recreational fisher) and obligatory discarding of ovigerous females (rare in shallow water). Because none of the fishing methods are 100% size or quota selective, some shallow-water S. verreauxi are discarded. Few quantitative commercial data are available, but Henry and Lyle (2003) estimated that recreational fishers nationally discarded 49% of their palinurid catches. Assuming a comparable trend in NSW, this would equate to ∼5000 recreationally discarded S. verreauxi; including a large proportion of shallow-water juveniles. Two inherent assumptions associated with such mandatory discarding are low associated fishing mortality and few deleterious sub-lethal impacts to discards.

Despite the need to elucidate the fate of discarded juvenile S. verreauxi, no scientific data have been collected. In fact, few studies have assessed impacts to discarded, trapped and hand-collected palinurids anywhere (but see Powrie and Tempero, 2009, Frisch and Hobbs, 2011). However, like other crustaceans caught by various fishing methods, which have been extensively studied (see Murphy and Kruse, 1995 for a review), the potential exists for some unaccounted fishing mortality and/or sub-lethal stress to unwanted individuals, with subsequent effects on biological processes. More specifically, previous studies have shown that negative impacts to discarded crustaceans typically are correlated to important and often cumulative factors, including their size (Brouwer et al., 2006), appendage loss (Uhlmann et al., 2009) or the fishing method (Powrie and Tempero, 2009) and/or the trap design (Butcher et al., 2012).

A major concern for discarded crustaceans is appendage loss, which often has a tractable relationship with reduced immunocompetence (Fotedar et al., 2001) or mortality (Uhlmann et al., 2009). In particular, loosing sensory or walking appendages can affect defence (Parsons and Eggleston, 2005), mobility and/or competitive ability (Juanes and Smith, 1995). Also, because crustaceans grow discontinuously, cumulative sub-lethal factors that affect ecdysial processes can alter moult increments (Juanes and Smith, 1995, Frisch and Hobbs, 2011) and ultimately reduce fisheries productivity. Mitigating such damage is considered important to reduce population and economic impacts (Parsons and Eggleston, 2007).

In addition to obvious physical damage, discarded crustaceans often incur physiological changes. Such alterations can be quantified by monitoring temporal changes in haemolymph constituents, including: protein (measured as refractive index – RI; Butcher et al., 2012); haemocyte counts (Jussila et al., 2001); clotting capacity (Fotedar et al., 2001); glucose (Paterson et al., 1997); lactate (Ridgway et al., 2006); calcium; magnesium; and potassium (Uhlmann et al., 2009). The utility of each parameter can be species-specific and generally depends on stressors inherent to a given fishing method (Butcher et al., 2012). Particular attention often has focused on haemocyte counts (Fotedar et al., 2001, Uhlmann et al., 2009) and glucose and lactate (Bergmann et al., 2001), which can positively correlate to hypoxia, handling and limb loss.

Given the above, two key aims of this study were to quantify the (i) relative size-selectivity associated with conventional trapping and hand collection of shallow-water S. verreauxi, and (ii) mortality, stress, physical damage and growth of discarded lobsters. Using this information, additional aims were to identify (iii) effective physiological stress indicators for future S. verreauxi studies and, where required, (iv) practical strategies to mitigate unaccounted fishing mortality and other negative impacts.

Section snippets

Control collection

Four to six weeks before starting the experiment, 22 juvenile S. verreauxi (80–110 mm CL) were caught from depths <10 m off Coffs Harbour (30°16′ S, 153°05′ E), NSW, Australia using rectangular traps (800 mm × 600 mm × 360 mm frame of 4 mm diameter (ø) steel rod (50 mm × 50 mm wire mesh), with two 190 mm × 145 mm side entrances of 50 mm wire mesh – Fig. 1a) baited with sea mullet (Mugil cephalus). Undamaged individuals were individually housed in 30 l polyvinyl chloride cages (0.3 m ø × 0.4 m depth; described by

Relative species, size, sex and moult selectivity

In total, 158 S. verreauxi were caught (Fig. 2), of which 25 (mean ± SD of 96.8 ± 15.6 mm CL) were from 157 deployments of round traps (relative catch-per-unit-of-effort (CPUE) of 0.16 per trap per 24 h), 36 (99.5 ± 9.2 mm CL) were from 119 deployments of rectangular traps (CPUE of 0.30 per trap per 24 h) in 1–4 m depth, with the remaining 97 (94.3 ± 19.4 mm CL) hand collected from 1 to 6 m deep (CPUE of 0.96 individual per diver per day). Bycatch comprised six blindsharks (Brachaelurus waddi; 420–510 mm total

Discussion

Quantifying unaccounted fishing mortality is difficult, but understanding the relative importance of the various subcomponents is essential to validate management controls enforcing size and species selectivity, and especially discarding (He, 2010). While the absence of any discard mortality in this experiment is positive, like in previous studies (e.g. Joll, 1977, Brock et al., 2003) there was within-trap predation which, along with the observed physical and, to a lesser extent, physiological

Acknowledgements

The study was funded by the NSW Recreational Fishing Trust, NSW Department of Primary Industries and Southern Cross University. Thanks are extended to K. James, K. Cowden, B. Burren, A. McManus, C. Barnes, M. Burns, J. Marshall, A. May, K. Rushworth and C. Tredinnick-Dawson for their technical assistance.

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