CHALLENGES AHEAD FOR AUSTRALIA'S GREY NURSE SHARKS
Dr. Kelli Anderson July 2013
In the past, it was estimated that almost thirty percent of the east coast’s grey nurse shark (GNS) population had been hooked by fishing equipment over the course of one year (Otway and Burke 2004). In a later study, the maximum percentage of sharks that had retained fishing gear or had fishing-related injuries for an individual sampling period was 29% for female and 52% for male sharks (Bansemer and Bennett 2010). Banning activities that impair the health and fitness of GNS in ecologically important areas is crucial for recovery of this critically endangered species. Due to the high incidence of GNS/fisher interaction, recreational fishing has been recognised and a major threat to GNS populations, and as such legislative changes have recently been made to marine zoning under the guise of improving protection for the species.
Fishing using baited hooks has now been banned in sanctuary zones, except for areas lying within 50 m of headlands and beaches. A study titled ‘Investigating the Behavioural Response of Grey Nurse Sharks to Recreational Lures and Baited Lines’ by Drs Will Robbins and Vic Peddemors (Cronulla Fisheries Research Centre of Excellence, 2011) showed that GNS actively take lines baited with blue mackerel ~35% of the time, and smaller pilchard/squid baits ~10% of the time when lines are placed 40 m from GNS aggregations. This implies that if baited line fishing occurs from beaches or headlands in close proximity to aggregating GNS populations, it is likely that GNS will interact with fishing gear whether the species is being specifically targeted or not.
Within sanctuary zones, recreational fishing using soft plastics, artificial and vegetable based baits, spinning and trolling with fly or artificial lures and jigging is allowed. The aforementioned study (Robbins and Peddemors 2011) found that GNS/fishing gear interactions did not occur when trolling using a range of plastic and metal lures. However, Bansemer and Bennett (2010) documented four GNS trailing/attached to lures during their study, which may have occurred as a result of the sharks targeting struggling fish caught via this method (i.e. not direct targeting of the lure its self). Therefore it is reasonable to suggest that fishing using lures may indirectly cause GNS/fishing gear interactions within the sanctuary zone. Furthermore, when performing necropsies of accidentally caught GNS, it was discovered that six out of eight sharks had internal hooks even though there was no external evidence of interaction with fishing equipment (Otway and Burke 2004). Thus, the true rate of shark/fishing gear interaction may be generally underestimated.
In the past, it was estimated that almost thirty percent of the east coast’s grey nurse shark (GNS) population had been hooked by fishing equipment over the course of one year (Otway and Burke 2004). In a later study, the maximum percentage of sharks that had retained fishing gear or had fishing-related injuries for an individual sampling period was 29% for female and 52% for male sharks (Bansemer and Bennett 2010). Banning activities that impair the health and fitness of GNS in ecologically important areas is crucial for recovery of this critically endangered species. Due to the high incidence of GNS/fisher interaction, recreational fishing has been recognised and a major threat to GNS populations, and as such legislative changes have recently been made to marine zoning under the guise of improving protection for the species.
Fishing using baited hooks has now been banned in sanctuary zones, except for areas lying within 50 m of headlands and beaches. A study titled ‘Investigating the Behavioural Response of Grey Nurse Sharks to Recreational Lures and Baited Lines’ by Drs Will Robbins and Vic Peddemors (Cronulla Fisheries Research Centre of Excellence, 2011) showed that GNS actively take lines baited with blue mackerel ~35% of the time, and smaller pilchard/squid baits ~10% of the time when lines are placed 40 m from GNS aggregations. This implies that if baited line fishing occurs from beaches or headlands in close proximity to aggregating GNS populations, it is likely that GNS will interact with fishing gear whether the species is being specifically targeted or not.
Within sanctuary zones, recreational fishing using soft plastics, artificial and vegetable based baits, spinning and trolling with fly or artificial lures and jigging is allowed. The aforementioned study (Robbins and Peddemors 2011) found that GNS/fishing gear interactions did not occur when trolling using a range of plastic and metal lures. However, Bansemer and Bennett (2010) documented four GNS trailing/attached to lures during their study, which may have occurred as a result of the sharks targeting struggling fish caught via this method (i.e. not direct targeting of the lure its self). Therefore it is reasonable to suggest that fishing using lures may indirectly cause GNS/fishing gear interactions within the sanctuary zone. Furthermore, when performing necropsies of accidentally caught GNS, it was discovered that six out of eight sharks had internal hooks even though there was no external evidence of interaction with fishing equipment (Otway and Burke 2004). Thus, the true rate of shark/fishing gear interaction may be generally underestimated.
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Most available studies that aim to address post-catch and release mortality in sharks have only focused on the short-term implications for animal health (over a few hours or days). Whether injuries or capture-stress have longer-term sub-lethal health and reproductive effects, or affect mortality rates is currently unclear. The limited data available from scientific studies where sharks have been caught and released suggest that post-release mortality rates may be less than 10% (for sharks in general). However the mortality rates of sharks released by recreational fishers is likely to be higher due to increased stress from extended capture times, rough handling, retained fishing equipment such as hooks and increased time out of the water (McLoughlin and Eliason 2008). In addition, sharks selected for capture and monitoring in scientific studies tend to include the healthiest individuals due to investment in expensive equipment. This suggests that the general health of sharks caught, and their subsequent condition at release by anglers would be more variable. The relationship between acute or chronic stress and general and reproductive health has been well studied for a variety of fish species. Generally speaking, the sub-lethal effects of stress can include reproductive impairment, changes in behaviour, infection, impaired immunity and lower growth rates (McLoughlin and Eliason 2008). In terms of injuries, interaction with fishing equipment that results in hooks being retained in the jaw can have varied consequences but injuries are often progressive (Bansemer and Bennett 2010, Fig. 1). Small or large hooks can cause severe jaw injuries that result in infection, necrosis and permanent disfigurement to varying degrees, while some small injuries are able to heal completely (Bansemer and Bennett 2010). In addition, a study on blue sharks from waters around Long Island (USA) has demonstrated that internal hooking can cause a range of health problems including oesophagitis, gastritis, hepatitis and proliferative peritonitis (Borucinska et al., 2002).
Figure 1: Time course of jaw injury on an individual mature male Carcharias taurus (ID#452) identified by its spot-patterns and a unique scar on its left flank. (a) Small hook (arrow) embedded in jaw hinge 4 July 2006, Fish Rock, (b) tissue necrosis extending from the site of the embedded hook 30 January 2007, Fish Rock, (c) healed injury site with likely permanent deformity 14 February 2008, Barge. Figure and legend sourced from Bansemer and Bennett (2010).
Grey nurse sharks are a slow-growing, take several years to become sexually mature and even in optimal circumstances only produce two pups every two years. Unfortunately, Australian GNS have a long history of over-exploitation that has resulted in a low effective population size. The life history traits of the GNS mean that populations are slow to recover, and even a low level of exploitation or mortality could cause a dramatic decline in the stability of the population (Dicken et al., 2007). This has broad implications for their conservation, and every effort must be taken to ensure that the recovery of this species is not compromised by legal or illegal activities and a lack of protection.
Information on protective measures
The current state of grey nurse shark protection (written July 2013)
Previous critical habitat site (2002) information can be found here :
NEW SOUTH WALES GOVERNMENT GAZETTE No. 237, Critical Habitat of grey nurse shark Notification 2002 under the Fisheries Management Act 1994. http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0003/381315/Grey-nurse-shark-critical-habitat.
Grey nurse sharks are a slow-growing, take several years to become sexually mature and even in optimal circumstances only produce two pups every two years. Unfortunately, Australian GNS have a long history of over-exploitation that has resulted in a low effective population size. The life history traits of the GNS mean that populations are slow to recover, and even a low level of exploitation or mortality could cause a dramatic decline in the stability of the population (Dicken et al., 2007). This has broad implications for their conservation, and every effort must be taken to ensure that the recovery of this species is not compromised by legal or illegal activities and a lack of protection.
Information on protective measures
The current state of grey nurse shark protection (written July 2013)
- The Bass Point critical habitat site has been delisted in accordance with recommendations from NSW DPI scientists. The shape of the Magic Point and Green Island critical habitat sites have been changed.
- The buffer-zone regulations that previously surrounded critical habitat sites are in the process of being revoked. Previously, all critical habitat zones were surrounded by a ‘buffer zone’ that extended a further 800 m from the edge of the critical habitat. The use of wire trace while fishing from a vessel that was anchored or moored was prohibited in buffer zones. However, wire trace could still be used with baited hooks from drifting vessels, both in buffer zones and critical habitat sites.
- The changes to the rules only affect recreational fishers and scuba divers. All methods of line fishing using bait (whether alive or dead, and excluding soft plastics, artificial and vegetable based baits) are prohibited within grey nurse shark critical habitat at Fish Rock, Green Island, and Magic Point, and waters within 200 m of specified coordinates at North Solitary Island, South Solitary Island and Mermaid Reef.
- Amnesty has been awarded to recreational line fishers who are able to fish from mainland beaches and headlands within sanctuary zones. For current zoning maps see http://www.mpa.nsw.gov.au. Further detail is provided below.
- All other recreational fishing activities will remain unaffected by the changes, including spinning and trolling with fly or artificial lure, use of soft plastics, jigging, crabbing, hand gathering and spearfishing (other than at Fish Rock).
- Existing spearfishing rules at grey nurse shark aggregation sites and critical habitats will not change other than at Fish Rock.
- For spearfishing, the existing regulations that have been in place since 31 July 1998 on the taking of fish within 500 m of the mean high water mark of Fish Rock will be reduced to align with the critical habitat of 200 m
- The taking of any fish by spear or speargun is prohibited within the critical habitat of grey nurse shark at Fish Rock other than: Australian salmon, Mahi Mahi, Tailor, Cobia, Marlins and Sailfish (all species in the family Istiophoridae), Mackerels and Tunas (all species in the family Scombridae), Wahoo, Trevallies, Yellowtail Kingfish and Rainbow Runner (all species in the family Carangidae)
- There are no changes to commercial fishing rules arising from the review of grey nurse shark protection.
- The existing Ocean Trap and Line Export Approval notifications continue to apply at North Solitary Island, South Solitary Island, Fish Rock, Green Island and Magic Point.
- The existing critical habitat diving regulations will be replaced by the national Code of Conduct for Diving with grey nurse sharks.
Previous critical habitat site (2002) information can be found here :
NEW SOUTH WALES GOVERNMENT GAZETTE No. 237, Critical Habitat of grey nurse shark Notification 2002 under the Fisheries Management Act 1994. http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0003/381315/Grey-nurse-shark-critical-habitat.
fURTHER rEADING
Bansemer, C. S. and Bennett, M. B. (2010) Retained fishing gear and associated injuries in the east Australian grey nurse sharks (Carcharias taurus): implications for population recovery. Marine and Freshwater Research 61: 97-103. View Article.
Borucinska, J. et al., (2002). Pathology associated with retained fishing hooks in blue sharks, Prionace glauca (L.), with implications for their conservation. Journal of Fish Diseases 25: 515-521. View Article.
Dicken, M.L., et al., (2007) Spatial and seasonal distribution patterns of juvenile and adult raggedtooth sharks (Carcharias taurus) tagged off the east coast of South Africa. Marine and Freshwater Research 58, 127-134. View Article.
McLoughlin, K. and Eliason, G. (2008) Review of information on cryptic mortality and the survival of sharks and rays released by recreational fishers. Australian Government: Bureau of Rural Science, SEDAR21-RD-22, 28pp. View Report.
Otway, N.M. and Burke, A. L. (2004) Mark-recapture population estimate and movements of Grey Nurse Sharks. Final Report to EnvironmentAustralia. Project No. 30786/87. NSW Fisheries Final Report Series No. 63. ISSN 1442-0147. 53pp. View Report.
Borucinska, J. et al., (2002). Pathology associated with retained fishing hooks in blue sharks, Prionace glauca (L.), with implications for their conservation. Journal of Fish Diseases 25: 515-521. View Article.
Dicken, M.L., et al., (2007) Spatial and seasonal distribution patterns of juvenile and adult raggedtooth sharks (Carcharias taurus) tagged off the east coast of South Africa. Marine and Freshwater Research 58, 127-134. View Article.
McLoughlin, K. and Eliason, G. (2008) Review of information on cryptic mortality and the survival of sharks and rays released by recreational fishers. Australian Government: Bureau of Rural Science, SEDAR21-RD-22, 28pp. View Report.
Otway, N.M. and Burke, A. L. (2004) Mark-recapture population estimate and movements of Grey Nurse Sharks. Final Report to EnvironmentAustralia. Project No. 30786/87. NSW Fisheries Final Report Series No. 63. ISSN 1442-0147. 53pp. View Report.