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ABSTRACT1. Little is known about the potential impact of habitat modification by bottom fishing gear on the growth of demersal fishes. An analysis is presented for the growth of blue cod in Foveaux Strait, southern New Zealand, based on otoliths of fish captured from two sites in Foveaux Strait in 1999.2. Each site contained two distinct areas of contrasting benthic habitat complexity, one area of relatively 'complex' recovering biogenic reef and another area of relatively 'simple' sand and gravel, both previously modified by oyster dredging.3. Data were fitted to von Bertalanffy growth models for each sex of blue cod from the four areas sampled. No significant difference in growth models was observed for either male or female blue cod compared between the two types of habitat complexity at the eastern site. However, growth differed significantly for both sexes of blue cod from the two habitat types at the western site. Pairwise t-tests further showed that growth differences only appeared biologically significant for the youngest blue cod sampled (3 years). These fish were, on average, 20% larger in complex biogenic reefs than in simple areas dredged by the oyster fishery.4. These results suggest that on-going disturbance and simplification of seabed habitat by the oyster fishery may impede the growth of juvenile blue cod. Areas of recovering biogenic reef may, therefore, provide important habitat for the recruitment and early development of blue cod in Foveaux Strait. Remedial actions may be required to protect some areas of recovering biogenic reef from further damage, and to allow dredged areas sufficient time to recover if the blue cod fishery and related resources are to be managed effectively.

Variability in the abundance of commercial catches of fish has been studied for centuries (Huxley, 1881), especially in highly productive and highly populated regions (Heincke, 1898;Newland, 1999).Globally, abundance of fishing stocks has displayed declines over the past several decades (Worm et al., 2009), with changes in commercial fish assemblages identified for important fishing grounds

Estimates of blue cod (Parapercis colias) relative abundance and population structure were made from potting surveys of Banks Peninsula and Dusky Sound, New Zealand in 2002. Five inshore and two offshore strata around Banks Peninsula, and five strata between the inner fiord and the open coast of Dusky Sound were surveyed. In Banks Peninsula the overall mean catch rate (all fish) was 2.13 kg/pot per h (range 0.04-4.74) and coefficient of variation (CV) was 10.8%. Blue cod from inshore strata were significantly smaller than those from offshore strata, catch rates were lower, and the sex ratio was skewed towards males (inshore 2.2:1, offshore 0.74:1). In Dusky Sound the overall mean catch rate was 2.69 kg/pot per h (range 1.28-8.42), CV was 6.3%, highest catch rates were on the open coast, and overall sex ratio was 0.78:1 (male:female). Blue cod in the 1940s from throughout New Zealand were on average larger than blue cod in Banks Peninsula and Dusky Sound during this survey. Low relative abundance and small size of blue cod from the more accessible inshore areas, is consistent with fishing pressure causing a reduction in size and probably abundance, particularly in Banks Peninsula inshore strata. In Banks Peninsula, sex ratios in inshore areas are skewed towards males, possibly a result of fishing pressure. The results support other studies on protogynous fish species in which the removal of the larger final sex fish (males), promotes sex inversion. The plasticity of the sex inversion means that blue cod may be capable of restoring optimal sex ratios in the natural state, but may overcompensate with size specific anthropogenic removal of large numbers of individuals that would otherwise inhibit the sex inversion process.

Recaptured eels examined for sex were all females, indicating that either eels differentiated into females because density was low, or that males moved out of the lake to more preferred habitat downstream. Tag retention was high and tagging had no adverse effect on growth. Enhancement or stocking with longfins is viable for low density recruitmentlimited, high country lakes, but growth is likely to be density dependent.Keywords longfin eel; coded wire tag; densitydependent growth; enhancement; sex ratio; dispersal Abstract Lake Hawea was stocked with c. 9500 juvenile longfinned eels (Anguilla dieffenbachii Gray) (mean weight 173 g) from the lower Clutha River of which a subsample of 2010 was tagged with coded wire tags. Three years later, the eel population in Lake Hawea was sampled resulting in 216 recaptures of transferred eels of which 42 were tagged. Eels had grown an average of 14 cm and 325 g (all recaptures). Growth rate of tag-recaptures averaged 4.1 cm year -1 , was linear and faster than pre-transfer when it was 2.4 cm year -1 (P < 0.01). Eels transferred into Lake Hawea experienced accelerated growth and increased condition ascribed to low density (density dependent) and abundant food. Eels dispersed throughout the lake, but density was highest adjacent to "the Neck", the point of release. Eels caught outside the Neck were larger and in better condition than those inside the Neckfurther evidence of density-dependent growth.

Hapuku (Polyprion oxygeneios) were tagged in south-east South Island (SESI), Cook Strait (CS), and Poor Knights Islands (PKI), New Zealand, to determine their movements. 1623 fish were tagged and the overall recapture rate was 16.3%. Some hapuku were recaptured from the tagging sites (SESI 13%, CS 39%, PKI 40%), often after long periods at liberty, whereas others travelled substantial distances. The greatest distance travelled was 1389 km (by two fish) and the maximum period at liberty was 10.2 years. SESI hapuku tended to migrate northwards towards CS. The median distance travelled increased with hapuku length at recapture, suggesting that maturation and spawning stimulate migration. However, some of the smaller, immature hapuku also travelled several hundred kilometres. CS hapuku appeared to travel much shorter distances than SESI hapuku, but this may have been an artifact of the lower hapuku fishing effort outside the CS-Kaikoura region. PKI hapuku showed very limited movements, and no interaction with CS or SESI fish. The results are consistent with the presence of a single stock in the SESI-CS region, and possibly a separate stock in northern New Zealand. M98026

Behavioral thermoregulation of New Zealand sea lions (Phocarctos hookeri) was studied at a male haul-out ground at Papanui Beach, Otago Peninsula, New Zealand. The proportion of time spent by sea lions in each of five postures (prone, curled, oblique, ventral-up, dorsal-up) and also with the number of flippers exposed or tucked (hind and fore) at different black-bulb temperature (T bb • C) ranges was recorded. Use of prone and curled postures (0-1 flippers exposed) declined as T bb increased, suggesting that these are adopted to conserve heat; oblique and dorsal-up postures (3-4 flippers exposed) use increased with T bb indicating a role in heat dissipation. The transition between heat conserving and heat dissipating postures occurred at about 14 • -20 • C (T bb ). Both foreflipper and hind flipper exposure increased with T bb and the trends were similar, but overall hind flipper exposure was 89% of foreflipper exposure. The results show that surface area of flippers exposed to air is largely controlled by postural adjustment. The increase in flipper exposure with T bb provides evidence of behavioral thermoregulation and that flippers are major sites for heat loss in the New Zealand sea lion, as observed for other otariid species. Nonpostural thermoregulatory behaviors such as flipper waving and sand flipping increased with T bb , and may provide additional means of dissipating heat. Total body surface areas of six sea lions ranged from 1.72 to 3.39 m 2 (curvilinear length range from 1.60 to 2.35 m), and total flipper surface area averaged 22.7% of total body surface area. As otariids do not employ their hind limbs for aquatic propulsion, their role in behavioral thermoregulation may provide an explanation for the relatively large size of the hind flippers of the New Zealand sea lion.

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