464 



Abstract— A critical process in assess- 

 ing the impact of marine sanctuaries 

 on fish stocks is the movement offish 

 out into surrounding fished areas. 

 A method is presented for estimat- 

 ing the yearly rate of emigration of 

 animals from a protected ("no-take") 

 zone. Movement rates for exploited 

 populations are usually inferred from 

 tag-recovery studies, where tagged 

 individuals are released into the sea 

 at known locations and their location 

 of recapture is reported by fishermen. 

 There are three drawbacks, however, 

 with this method of estimating move- 

 ment rates: 1) if animals are tagged 

 and released into both protected and 

 fished areas, movement rates will be 

 overestimated if the prohibition on 

 recapturing tagged fish later from 

 within the protected area is not made 

 explicit; 2) the times of recapture are 

 random; and 3) an unknown propor- 

 tion of tagged animals are recaptured 

 but not reported back to research- 

 ers. An estimation method is pro- 

 posed which addresses these three 

 drawbacks of tag-recovery data. An 

 analytic formula and an associated 

 double-hypergeometric likelihood 

 method were derived. These two 

 estimators of emigration rate were 

 applied to tag recoveries from south- 

 ern rock lobsters (Jasus edwardsil) 

 released into a sanctuary and into 

 its surrounding fished area in South 

 Australia. 



Estimating the emigration rate of fish stocks 

 from marine sanctuaries using tag-recovery data 



Richard McGarvey 



Aquatic Sciences, South Australian Research and Development Institute (SARDI) 



2 Hamra Avenue 



West Beach, South Australia 5024, Australia 



E-mail address; mcgarvey nchardia saugovsa gov.au 



Manuscript submitted 24 March 2003 

 to Scientific Editor's Office. 



Manuscript approved for publication 

 5 March 2004 by the Scientific Editor. 

 Fish. Bull. 102:464-472(20lili 



Marine sanctuaries, also known as 

 marine protected areas (MPAs), ma- 

 rine reserves, and no-take areas, are 

 being widely promoted and imple- 

 mented. Important for assessing the 

 impact of these "no-take" sanctuaries 

 (from which fishing has been excluded I 

 on exploited populations is the rate 

 of emigration of animals out into the 

 remaining fished habitat. 



The most widely available data for 

 estimating movement rates of com- 

 mercially or recreationally exploited 

 populations are those from tagged 

 and recovered fish (Hilborn, 1990). 

 Animals are captured alive, a visible 

 numbered tag is inserted and they 

 are released back into the wild. Be- 

 cause the accuracy of tag-recovery 

 studies relies on fishermen reporting 

 recaptured tags, the quality of tag-re- 

 covery information is lower than that 

 from a controlled experiment. 



Tag-recovery experiments have 

 three limitations for estimating move- 

 ment rates of animals — the first two 

 apply to most tagged populations, the 

 third applies specifically to emigra- 

 tion from sanctuaries: 1) times at 

 large (the numbers of days from when 

 each animal is tagged and released to 

 when it is subsequently recaptured 

 in the fishery) are highly variable; 2) 

 not all recaptured tags are reported 

 to researchers by fishermen and this 

 rate of tag nonreporting is often un- 

 known; and 3) tag recoveries cannot 

 be obtained from within sanctuaries 

 for the simple reason that no fishing 

 is allowed there. 



If this last asymmetry (of recap- 

 tures from the sanctuary coming only 

 from tagged animals that emigrate) 

 is not accounted for in the estimation 

 model, then the emigration rate out of 



the sanctuary will be overestimated. 

 With previous movement estimators, 

 tag releases and recaptures from all 

 strata have been assumed. The aim 

 of the present article is to develop an 

 unbiased estimator of emigration rate 

 from no-take areas by using data of 

 tag releases both into the sanctuary 

 and into the fished zone surrounding 

 it, but where recoveries from nonmov- 

 ing tagged animals are only possible 

 from the fished zone. An estimate for 

 the recovery rate (proportion of fish 

 recaptured and their tags reported) in 

 the fished zone was also obtained. 



Materials and methods 



Tag-recovery data 



The data used to estimate the emi- 

 gration rate from Gleesons Landing 

 Lobster Sanctuary (Fig. 1) are tag 

 recoveries from lobsters tagged and 

 released both inside the sanctuary 

 and into the fished zone surrounding 

 the sanctuary. A large South Aus- 

 tralian lobster tagging program was 

 undertaken in 1993-96 throughout 

 South Australian waters. T-bar tags 

 (Hallprint, Victor Harbour, South 

 Australia) were inserted into the 

 ventral muscle at the first segment 

 of the lobster abdomen. The rate of 

 tag shedding was estimated from 

 double tags at between 6 f r and 1292 

 per year (Xiao 1 ) and is incorporated 

 in the recovery rate. 



Xiao Y. 2003. Personal commun. 

 Aquatic Sciences, South Australian 

 Research and Development Institute 

 (SARDI), P.O. Box 120. Henley Beach, 

 South Australia 5022. Australia. 



