Determination of paua growth in PAU 2, SA, SB, and 5D

Transcription

1 MINISTRY OF FISHERIES Te Toufiuki i nga tini o Tongoroo Determination of paua growth in PAU 2, SA, SB, and 5D J. R Naylor N. L. Andrew New Zealand Fisheries Assessment Report August 2002

2 Determination of paua growth in PAU 2,5A, SB, and 5D J. R Naylor N. L. Andrew NTWA PO Box Wellington New Zealand Fisheries Assessment Report August 2002

3 Published by Ministry of Fisheries Wellington 2002 ISSN Ministry of Fisheries 2002 Citation: Naylor, J.R.; Andrew, N.L. (2002). Determination of paua growth in PAU 2,5A, 5B, and 5D. New Zealand Fisheries Assessment Report 2002/ p. This series continues the informal New Zealand Fisheries Assessment Research Document series which ceased at the end of 1999.

4 EXECUTIVE SUMMARY Naylor, Jm Andrew, N.L. (2002). Determimation of paw growth in PAU 2,5& 5B, rmd 5D. New Zealand Fuheries Asse~~m~t Report 200U34.14 p. We present estimates of growth in PAU 2, SA, 5B, and 5D. There were no previous estimates of paua growth in PAU SA and 5D, and growth estimates in PAU 2 and SB were based on only one site in each area The growth information smnmarised here and fisheryderived data are used as inputs to the assessments of PAU SB and PAU SD.

5 1. INTRODUCTION 1.1 Overview Previous estimates of growth for PAU 2 and PAU 5B were poor, and based on only one site in each area There were no growth estimates for PAU 5A or PAU 5D. Because of the high spatial variation in growth in paua (e.g., Sainsbury 1982, McShane & Naylor 1995), management models may previously have been based upon biologically inappropriate information. Improved growth estimates have since been obtained at several sites in PAU 2, 5A, 5B, and 5D and are presented here. 1.2 Study sites Paua were tagged at three sites in each of PAU 2, PAU 5A, and 5B, and two sites in PAU 5D (Figure 1). In PAU 2, tag returns h m one site north of Castle Point were so low that they provided no useful growth information. To provide a more complete estimate of growth within this QMA, we have data from a previous study at Breaker Bay near Wellington (Figure 1). In PAU 5A, paua were tagged near the entrance to Poison Bay and on the northern and southern entrance to Chaw Inlet (Figure 1). In PAU 5D, paua were tagged in both the Catlins East and Catliis West research strata. Study sites in PAU 5B were selected to span the &ge of conditions on the east coast of Stewart Island from Christmas Village in the north to Port Adventure in the south. There is one previous growth estimate for Waituna on the west coast of the island (see Table 3). 2. METHODS 2.1 Estimation of growth Growth estimates were derived from mark-recapture methods. More than 500 emergent and cryptic paua across the available size range were collected from each site (Figure 1, Table 1). Paua were tagged with numbered 6 mm diameter polyethylene discs attached next to the spire of the shell with cyanoacrylate glue. The shells were cleaned of epibiota if necessary, and lightly dried with a towel. Emersion times were minimised and always less than 1 hour. Tagged paua remained at liberty for about one year and were then recovered by thorough searching at and around each site. Shell lengths of recovered paua were measured to the nearest millimetre. Growth of recaptured paua was estimated using the maximum likelihood approach of Francis (1988, 1995). This model expresses observed increments in length as functions of the observed length at tagging and time at liberty, and describes growth in terms of average annual growth for individuals of a given size (Francis 1988). Parameters estimated during this process included the mean kual growth rates at two lengths, parameters for growth variability, and the influence of outliers in parameter estimation. Four growth models describing growth variability (equations 5-8 of Francis 1988) were fitted to the data. The lengths used to compare growth rates among sites were chosen after inspection of the length-frequency distributions of recaptured tagged paua. To facilitate comparison with previously published estimates of paua growth, the usual von Bertalanffy growth parameters (K and Lm) were also estimated (using equation 1, Francis 1988).

6 3. RESULTS 3.1 Growth The numbers of paua tagged and recaptured and the time at liberty at each site is shown in Table 1. Fewer than expected tagged paua were recovered from the two sites near Mataikona and the Twakirae site. Migration, recreational harvest, and the cryptic habitat provided by the reef may have contributed to these low recoveries. Incremental growth of paua recaptured in PAU 2, 5A, 5B, and 5D is shown in Figures 2-5 respectively. Mean annual growth estimates at length and von Bertalanm growth parameters are shown in Table 2. Some negative growth associated with measurement error or shell damage was recorded and is included in the analyses. Using GROTAG (Francis 1988), the model estimated the mean annual growth rates at two lengths, with parameters to estimate the influence of outliers and growth variability (according to equation 5 of Francis 1988). The introduction of more complex relationships describing gmwth variability (equations 6-8 of Francis 1988) occasionally resulted in a significant improvement to the model fit. Mean annual growth estimates at lengths a and P, the growth variability equations used in their estimation, and the von Bertalanfi growth parameters derived from these are shown in Table 2. The addition of Francis's (1995) general growth model did not significantly improve the fit of the model to any of the tag recapture data sets. For Mataikona (Figure 2), the model was sensitive to the starting values of a and P, indicating that growth was not well described by the model. 4. DISCUSSION The estimated asymptotic lengths of paua from tagging sites ranged from 125 mm at Mataikona to about 154 mm at the Catlins West and Landing Bay sites. The Mataikona data set is relatively small however, and asymptotic length in PAU 2 is likely to be better reflected in the Turakirae and Breaker Bay data sets, where similar von Bertalanffy growth parameters were estimated (Table 2). Asymptotic lengths for sites in PAU 5B ranged between 130 and 140 mm (Table 2) and are lower than the estimate reported for the west coast of the island at Waituna (Table 3). The associated estimates of the Brody growth coefficient (K) in PAU 5B are unusually high (see Table 2) and are likely to be an artifact of the tag recapture data (Figure 4) where very few large paua were recaptured. The estimated grdwth parameters reported here do not appear consistent with observed length-frequency distributions from PAU 5B (Breen et al. 2002a). Growth is estimated within the model used to assess the PAU 5B fishery, and is estimated from all available information, including the length-frequencies. The estimates of asymptotic size and K derived from this process were mm and 0.26 respectively (Breen et al. 2002a). These estimates appear more credible. Mark-recapture and model-based estimates of growth in PAU 5D also differed, but by considerably less (150.3 vs 154.5, and 0.32 vs 0.34). The closeness of the two estimates probably reflects the wider size range recaptured in PAU 5D than in PAU 5B. With the exception of Turakirae and Breaker Bay, the estimated asymptotic lengths for sites (see Table 2) are supported by the respective length frequencies of tagged paua (Figure 6). The growth information summarised here and fishery-derived data are used as inputs to the assessments of PAU 5B and PAU 5D (Breen et al. 2002a, 2002b).

7 5. ACKNOWLEDGMENTS We are grateful to Pete Notman, Owen Anderson, and Chazz Maniot for assistance in the field, and to Pete Notman and Peter Gerring for assistance with the graphics. This work was funded by the Mistry of Fisheries, project PAU REFERENCES Breen, P.A.; Andrew, N.L.; Kim S.W. (2002a). The 2002 stock assessments of paua (Haliotis iris) in PAU 5B. Final Research Report to the Ministry of Fisheries. 55p. Unpublished report held by the Ministry of Fisheries, Wellington. Breen, P.A.; Andrew, N.L.; Kim S.W. (2002b). The 2002 stock assessments of paua (Haliotis iris) in PAW 5D. Fi Research Report to the Ministry of Fisheries. 51p. Unpublished report held by the Ministry of Fisheries, Wellington. Francis, R.I.C.C. (1988). Maximum likelihood estimation of growth and pwth variability from tagging data. New Zealand Journal of Marine and Freshwater Research 22: Francis, R.I.C.C. (1995). An alternative mark-recapture analogue of Schnute's growth model. Fisheries Research 23: McShane, P.E.; Naylor, J.R. (1995) Small-scale spatial variation in growth, size at maturity, and yield- and egg-per-recruit relations in the New Zealand abalone Hdiotir iris. New Zealand Journal of Marine and Freshwater Research 29: McShane, P.E.; Mercer, S.; Naylor, J.R.; Notman, P. (1996) Paua (Haliotis iris) fishery assessment in PAU 5, 6, and 7. New Zealand Fisheries Assessment Research Document p. Unpublished report held in NIWA library, Wellington. Naylor, J. R.; Nohnan, P. R; Mercer, S. F.; Gerring, P. (1998). Paua (Haliotis iris) fishery assessment in PAU 5, 6, and 7. New Zealand Fisheries Assessment Research Document p. Unpublished report held inniwa library, Wellington. Poore, G.C.B. (1972) Ecology of New Zealand abalones, Hdiotis species (MoUusca: Gastropods). 3. Growth. New Zealand Journal of Marine andfreskwater Research 6: Sainsbury, K.J. (1982). Population dynamics and fishery management of the paua, Haliotis irk Population structure, growth, reproduction and mortality. New Zealand Journal of Marine and Freshwater Research 16: Schiel, D.R; Breen, PA. (1991). Population structure, ageing, and fishing mortality of the New Zealand abalone HaIiotis iris. Fishery Bulletin 89:

8 Table 1: Number of paua tagged and recaptured and time at liberty. QMA Site Number tagged Number recovered % recovered PAU 2 Turakirae PAU 2 ~ataikona PAU2 BreakerBay PAU 5A Poison Bay PAU 5A Landing Bay PAU 5A Red Head Point PAU 5B Christmas Village PAU 5B Ocean Beach PAU 5B Port Adventure PAU 5D Catlins East PAU 5D Catlins West Days at liberty Table 2: Mean annual growth estimates (mmlyear) of paua at lengths a and $,and von Bertalanffy growth parameters from sites in PAU 2, PAU 5B and PAU 5D. Growth Site Mean Mean variability growth (gw) growth (g 11s) model Lm K Turakirae Mataikona Breaker Bay Poison Bay Landing Bay Red Head Point Christmas Village Ocean Beach Port Adventure Catlins East Catlins West Table 3: von Bertalanffy growth parameters of paua sampled at other sites around New Zealand. Area K L, Source Peraki Bay Sainsbury (1982) Kaikoura Poore (1972) Kaikoura Poore (1972) D'Urville McShane & Naylor (1995) D'Urville Schiel & Breen (1991) Kahurangi Naylor et al. (1998) Waituna McShane et al. (1996) Marlborough Schiel & Breen (1991)

9 PAU 5A J' Poison Bay Yankee River i L Christmas Village PAU 5D Ocean Beach East Cape Port Adventure - 1Obn *\wallace / Porpoise Bay - 10 km Nugget Point Head Figure 1: Map showing the study sites in PAU 2,5A, SB, and 5D.

10 45 [ Turakirae Mataikona.. Breaker Bay Shell length (mm) Figure 2: Incremental growth of paua tagged and recaptured from sites in PAU 2.

11 45 r Poison Bay Red Head 35 Landing Bay Shell length (mm) Figure 3: Incremental growth of paua tagged and recaptured from sites in PAU 5A.

12 65 [ Christmas Village Ocean Beach F r Port Adventure Shell length (mm) Figure 4: Incremental growth of paua tagged and recaptured from sites in PAU 5B.

13 1. Catlins East % 45 r Catlins West Shell length (rnm) Figure 5: Incremental growth of paua tagged and recaptured from sites in PAU 5D.

14 14 1 Breaker Bay 14 1 Poison Bay 1 Christmas Village Ocean Beach Length (mm) Figure 6: iength frequency distributions of paua tagged at sites in PAU 2,5A, 5B, and 5D.

15 14 1 Port Adventure Catlins East 10 4 Catlins West 12 Length (mm) Figure kont': Length frequency distributions of paua tagged at sites in PAU 2,5A, SB, and 5D.