Use of binary and truncated regression models in the analysis of recreational fish catches

Abstract

Estuaries provide one of the most popular areas for commercial and recreational anglers to fish. At present, no estuary-specific study of recreational fisheries resources has been attempted in southern Queensland, Australia. The work reported in this thesis provides a detailed analysis on the recreational catch of the yellowfin bream (Acanthopagrus australis), dusky flathead (Platycephalus fuscus) and sand whiting (Sillago ciliatd) resources in the Burnett River, Maroochy River and Pvmiicestone Passage. Recreational fishing data typically contain a large proportion of zero values and show variability or dispersion greater than that allowed for in many standard regression models (eg Normal and Poisson) and the assumptions required for these analyses will not be valid. In this thesis a two stage regression approach involving a binary (non-zero/zero catch) response and the non-zero catches was used for analysing recreational fish catches to account for the extra zeros and over-dispersion present in the data. Also, the statistical bootstrap method was utilised to estimate confidence intervals on total recreational catch given the large proportion of zero catches. Unlike the Queensland commercial fisheries, which provide catch returns, the recreational catch was unknown and needed to be estimated. Recreational catch and fishing effort data from roving creel surveys were collected between June 1997 and August 1998. This method involved a person on the water counting and interviewing boat and shore fishers at a variety of locations and times. The number of people fishing and the resulting harvest differed between estuaries. More people fished during winter than at any other time of the year. Annual recreational fishing effort was of the order of 13 000 angler visits to the Burnett River, 28 000 to the Maroochy River, and 41 000 to the Pumicestone Passage. Catch rates were generally less than one fish per group fishing hour. Binary and truncated regression models were effective in analysing the catch data, which exhibited many zero values. Boat fishing groups with large numbers of anglers were less likely to catch fish than smaller groups. However, groups with more fishing lines had more chance of catching fish compared to similar sized groups with fewer lines. Estimated daytime recreational catch of yellowfin bream, dusky flathead and summer whiting was greater in Pumicestone Passage than in the Maroochy River or Burnett River. A summary of estimated total recreational catches is given in Table 1. The results highlight the magnitude of recreational fishing in Australian estuaries, and reinforce the concept that future assessment of fish stocks should include the recreational fishery.Table 1 Summary of total recreational catch estimates. Note: Recreational catch was estimated for the daytime period 6am to 6pm from September 1997 to August 1998 (95% bootstrap confidence intervals shown in parentheses). Burnett River Maroochy River Pumicestone Passage Fishing Effort Recreational (daily boat numbers) 10(8-11) 15(13-18) 43 (38-49)Recreational {daily shore fisher numbers) 17(14-20) 48 (43-54) 27 (22-33)Yellowfin bream Recreational Catch (tonnes) 5.5 (4.4-6.7) 12.9 (9.6-17.0) 22.7(19.1-27.0)Dusky Flathead Recreational Catch (tonnes) 2.6(1.8-3.3) 2.3(1.4-3.1) 10.6(7.9-13.0)Summer Whiting Recreational Catch (tonnes) 1.4(1-1.9) 5.2 (4.2-6.2) 9.8(8.1-11.7)