Marine reserves and the spiny lobster, Jasus edwardsii

The impact of no-take marine reserves on spiny lobster, Jasus edwardsii, populations and the adjacent lobster fishery was assessed in a study that determined: the response of lobster populations to protection, if lobsters within marine reserves moved out into the surrounding fishery, examined the behavioural characteristic of lobsters that contributed to their recovery and spillover, and contrasted catch characteristics around a north-east New Zealand marine reserve with 2 unprotected sites. Surveys of 4 no-take marine reserves of different ages and 4 unprotected control sites confirmed that -I edv,ardsii increase in mean size and abundance within protected areas. Total lobster densiry was estimatedto increase by 6.1% peryearof protection. The relationship bet*'een age of reserve and the density of lobsters above the legal size timit (>100 mm carapace lenglh) was complicated by depth related interactions between reserves, due to seasonal changes in the depth distribution of lobsters and differences in the timing of surveys among locations. However, density increases in legal sized lobsters were greater than those of the overall population. Mean size of protected lobsters increased in a non-linear fashion, reflecting the asymptotic growth characteristics of the species. Mean carapace length of lobsters increased by | |. 24 mm after 3 years of protection and only by 16,25 mm after2l years of protection. Corresponding increases in biomass (kg.500 m-2) and egg production (eggs.500 *'t) were estimated to be 7.4Yo and 6.60/o respectively per year of protection. A tag recapture program indicated that the limited scale of movements and relatively high site fidelity of mature J. edwardsii aided the recovery of lobster populations in protected areas. Of 737 lobsters tagged in and around the Leigh Marine Reserve,212 were subsequently resighted. Seventy percent of resighted lobsters were relocated less than 250 m along the shore from their initial site after a mean period of liberry of 146 (se : 13.42) days. However, seasonal offshore movements took lobsters beyond the seaward boundary of the reserve where they were susceptible to capture. Of the 521 lobsters tagged on inshore reefs within the Leigh Marine Reserve. l.9o% were caught over the seaward boundary by commercial fishers, nd 14.4% of the I 8l lobsters tagged over the seaward boundary were resighted on inshore reefs within the reserve. Movements into or out of the reserve across the longshore boundaries were also recorded for 7 out of the 27 lobsters moving further than 250 m along the shore. Acoustic tracking confirmed that J. edwardsii have a high site fidelity, with tracked lobsters spending a median of 84Yo of their time at their home site. Twenty one percent of the 26 lobsters fitted with acoustic tags never left their tagging site and, of those that did leave 560/o eventually returned. l,obsters moved up to 3. I km away from their home sites but managed to find their way back after periods of I to 103 days away. Five lobsters had strong associations with two separate sites and made repeated movements between these alternate home sites. The straight line distance between alternate home sites ranged from 200 m to 1.3 km, and the period between visits to their primary or secondary home sites ranged from I to 93 days. Movement activity varied throughout the year, and seasonal patterns differed between males and females. Females displayed one peak in movement activity per year, around the time of larval release in September-October. Males displayed a summer peak centred on January, and a winter peak centred on July. The onset of high movement activity was often accompanied by a shift to deeper water and l0 of the 14 lobsters tracked for over 6 months spent periods away from the inshore reef system. Exposed groups of lobsters were observed aggregating in offshore areas of sand and low lying patch reef during the day. Offshore aggregations were observed over 7 months of the year and lobsters within the aggregations displayed behaviour consistent with the use of mutual defence. The sexual composition of the aggregations reflected seasonal patterns in male and female movement rates. Male . /. ehuqrdsii dominated the aggregations in winter and summer; times rvhen peak feeding rates of males held in captivity rvere also recorded. Females dominated the offshore aggregations in September-October when larvae are released. Seven of the 26 lobsters fitted with acoustic tags moved over the boundaries of the Leigh Marine Reserve and Tawharanui Marine Park during offshore movements. Despite the fact that there is no fishing access to inshore reefs within the Leigh Marine Reserve, no significant difference was detected between the catch per unit effort (kg.trap haul-r) of lobsters caught around the reserve, nearby coastal Leigh or Little Banier Island. However, catches around the marine reserve contained fewer (P:0.0009) but larger lobsters than at Little Barrier Island. The catch characteristics of lobsters from coastal Leigh were intermediate between the other two sites. As access to inshore reefs around the Leigh Marine Reserve was limited to a small area at either end of the reserve, traps tended to be set in offshore locations and the sexual composition of the total catch around the Leigh Marine Reserve reflected the seasonal movements of males and females into, and out o{ offshore areas. At coastal Leigh and Little Banier Island the location of traps was not restricted and greater use was made of coastalfringing reefs. As a result the sexual composition of the catch at these locations did not reflect the movement of various componcnts of the lsbster populatlon into and out of specific habitats ,or losatious; Overall, the results of this shrd5r ,ssgg6s1 that relatlvely small (5 kmz) no-take marine res€ffes inerese lobster bismass and e@ production, without adversely affecting oateh rates in the surrounding fishery'. Marine regelves may there.fore rcprcrent a viable management tool, which if ,used in oorrjunetioa wi$ othermanagement rogimes, could provide a more precautionary approach'to the management of theJ e4wardsii fishery at mlni'qal agst to the industry.