Blue Cod in the Marine Reserve

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Blue Cod – Numbers Building and Spreading Photo: Malcolm Francis

 

This serves as an introduction to a note from one of the graduate students at Victoria University’s marine sciences group. Blue Cod is an important species in the New Zealand marine environment. Highly prized by both commercial and recreational fishers for its eating quality, blue cod are obviously under pressure especially at inshore habitats. Some fisheries have had to be closed and all have limits imposed on catch size and number. Blue cod are frequently one of the key indicator species of recovery or change in marine reserves after establishment, and prove amenable to monitoring and for research.

 

Blue cod, Parapercis colias, is a temperate marine fish of the weever or sand perch family Pinguipedidae. It is also known variously as New Zealand cod, or its Māori names rawaru and pakirikiri. It also can have local names, such as Akaroa Blue Cod, though there are few legal sized blue cod left in that harbour. It is not a true cod, as occurs in the North Atlantic, but may be better called a sand perch.

It is exclusively found in New Zealand in shallow waters around the rocky coasts to depths of 150 m, though it is far more common south of Cook Strait. It is brown, bluish green or blue black above with white toward the belly. Large examples are usually greenish blue in coloration, while smaller ones are blotched in varying shades of brown. An adult may grow to 65 cm in length and weigh from one to three kilograms. It feeds mainly on small fish and crabs. Blue cod are strongly territorial. Spawning takes place in southern spring and fish can also change sex from female to male, in common with a number of other fish.

Blue Cod are a plump fish which produces good fillets, with very low oil content. It is an important recreational species in the South Island and is commercially harvested. Blue cod populations are supposed to be managed sustainably under New Zealand’s fisheries quota management system, although they are becoming scarce in many areas due to fishing pressure. Annual commercial catch range is between 1,300 and 2,000 tonnes.

The unknown sustainability of current catch limits, which are significantly greater than yield estimates based on past average catches, the combined commercial and recreational catches plus limited research all give cause to be concerned.   Large and heavily baited cod pots, which take most of the commercial catch, can damage seafloor species when dropped in deeper waters. Other concerns include shags being caught in pots, and the lack of a national management plan. 

The blue cod fishery in the Marlborough Sounds is one of the iconic recreational fisheries in New Zealand. However, there have been long-standing concerns about the sustainability of blue cod within the Sounds. The fishery was closed in 2008, after NIWA survey results had shown blue cod in the Marlborough Sounds Area declined substantially (by an estimated average of 64 per cent) between 1995/96 and 2004. From 2004 to 2007, the population either continued to decline or remained at low levels in the inner, middle and outer parts of Queen Charlotte and Pelorus Sounds. It has now been reopened with very low bag limits.

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A glowering group of blue cod massed on a sandy seabed    Photo M. Francis

Fishers say that, in Fiordland and at the Chatham Islands, one is struck by the comparative size of the blue cod together with their considerable abundance. They are voracious feeders often being the first species caught when baited hooks are lowered to the bottom in any new fishing spot. This perhaps goes a long way to explain why they are so easily fished out by recreational anglers from certain localities! Perhaps fishing in Fiordland is an echo of the similar abundance of cod in the Sounds and other popular fishing spots years ago. Blue cod are found mostly amongst reefs and over sand and cobbles from a few metres down to about 150m. The Pegasus Canyon off Canterbury produces some very big blue cod, as does the Kaikoura coast and Motunau Beach.

Blue Cod are inquisitive fish and will often approach divers and bite their fingers with their lippy mouths. Commercial fishing boats target them around the south-eastern coast and the Chatham Islands, where they are caught in pots like crayfish. With their beautiful steely blue colouration the fish are a feature of considerable appeal to recreational snorkelers and divers.

(Sources: Wikipedia, Te Ara Encyclopaedia of NZ, Ministry of Primary Industries, Forest and Bird, Fishingmag.com)

With this background it is easy to appreciate the interest in the species in marine reserves. There has been much debate over the value of marine reserves as a recovery source of fish for the surrounding marine environment over time. There is much anecdotal evidence from fishing preference behaviour and increasingly from empirical research to support the view that, not only do some fish and other marine critters increase in numbers and size within a marine reserve established in a highly fished area, but also that fish move out of the reserve to the benefit of surrounding waters and eager fishers. Blue cod are known to have quite a territorial or sedentary habit, compared with snapper which generally range far and wide, though like snapper, cod can also range wide at some time in their life cycle. Can blue cod also spill over into waters outside the protection of a marine reserve and thus be available for fishers? 

Note by Daniela Díaz-Guisado 

“I am a Chilean student studying for my PhD at Victoria University of Wellington. I studied marine biology in Chile and came to New Zealand looking for the opportunity to work in marine conservation, attracted by the well-developed field of study.  My experience in New Zealand will be very important to my future career and I hope to apply what I have learnt in NZ back in my home country. 

My current project focusses on blue cod (Parapercis colias), a species endemic to New Zealand waters and one of the most popular coastal fish species in the country. Blue cod have been heavily fished over the years and had showed signs of recovery (increase in size and abundance) inside marine reserves. I have carried out several fieldwork surveys in the Taputeranga Marine Reserve to evaluate the effect of the reserve on the abundance and size of blue cod. My general aim is to detect spillover (juvenile and adult movement) from the marine reserve to adjacent non-protected populations. The methods that I have used include a Baited Underwater Video methodology (remotely operated video camera), an Underwater Visual Census (diver observation) and also a tagging survey to detect differences in abundance and size of fish between reserve and non-protected areas, and also to evaluate the movement patterns of the fish across reserve boundaries. An important part of my research is related to the fact that the Taputeranga Marine Reserve is one of the few reserves worldwide that had a baseline study performed before the establishment of the reserve in 2008, allowing a more adequate approach for the detection of changes due to reservation status. 

I am now close to finishing my studies. My preliminary results suggest that there is a positive reserve effect on the abundance and size of blue cod – we see more blue cod and they are on average bigger inside than outside the reserve. Also the tagging survey provides evidence of patterns of movement of blue cod that have not been described before. For example, I recaptured fish that have moved over 150 km away from the tagging location and several of those fish have moved from the reserve to non-protected areas.

Diving Daniela

Diving at Taputeranga Marine Reserve.

Fieldwork

Fieldwork at Taputeranga Marine Reserve  (Orca in background)Photos: Daniela

 

Overall, my research shows that the Taputeranga Marine Reserve is having an important conservation effect on the local population of blue cod. Fish are bigger and more abundant, plus they are moving along the south coast (and further afield) and are hopefully adding to populations elsewhere.” 

Daniela’s research results provide a ‘yes’ answer to the question on blue cod ‘spill over’. Her final results and published material will be studied with interest as yet further empirical evidence of the value of marine reserves to fishing, as well as for nature conservation.