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Measuring the effect of anthropogenic change on cetacean populations is hampered by our lack of understanding about population status and a lack of power in the available data to detect trends in abundance. Often long-term data from repeated surveys are lacking, and alternative approaches to trend detection must be considered. We utilised an existing database of linetransect survey records to determine whether temporal trends could be detected when survey effort from around the world was combined. We extracted density estimates for 25 species and fitted generalised additive models (GAMs) to investigate whether taxonomic, spatial or methodological differences among systematic line-transect surveys affect estimates of density and whether we can identify temporal trends in the data once these factors are accounted for. The selected GAM consisted of 2 parts: an intercept term that was a complex interaction of taxonomic, spatial and methodological factors and a smooth temporal term with trends varying by family and ocean basin. We discuss the trends found and assess the suitability of published density estimates for detecting temporal trends using retrospective power analysis. In conclusion, increasing sample size through combining survey effort across a global scale does not necessarily result in sufficient power to detect trends because of the extent of variability across surveys, species and oceans. Instead, results from repeated dedicated surveys designed specifically for the species and geographical region of interest should be used to inform conservation and management.

The proportion of mature fish at age or length is one of the most important population attributes in assessing reproductive potential. This proportion is usually named the maturity ogive. The most crucial step in estimating this proportion deals with maturity staging assessed by macroscopic or histology analysis. Macroscopic analysis is relatively inexpensive but usually introduces large amount of error. Histology is the most accurate method for maturity staging but is expensive and time consuming. Here, we propose using the gonadosomatic index (GSI) as an alternative way to estimate the maturity ogives. A logistic multinomial model was implemented to separate immature, mature-active, and mature-inactive fish, based only on their value of GSI. We evaluated the performance of the GSI-based method by comparing the results with ogives estimated from macroscopic and histological staging using the extensive database available for Chilean hake (Merluccius gayi gayi). Maturity ogives from GSI analysis were evaluated at the start and end of the reproductive season. Results showed that, in all cases analysed, maturity ogives from GSI were closer to the ogives based on histology than those from macroscopic staging. Comparing across periods, those maturity ogives computed at the start of the reproductive season give estimates very similar to those from histological staging. To have unbiased estimates of maturity ogives from GSI analysis, we recommend using data from the start of the reproductive season to minimise the frequency of spent fish. In addition, the assumption of the isometry between gonad and gutted weight across maturity stages needs to be tested before the use of this GSI method. The analyses presented here provide a promising method to estimate maturity ogives when histological staging data are lacking or when macroscopic analysis is suspected to have large amounts of errors.

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Summary The total length (TL) at sexual maturity by sex, fecundity characteristics, and some population aspects (size structures and sexual proportions) are presented for the yellownose skate, Dipturus chilensis, in the eastern South Pacific Ocean. Samples were taken between January 2003 and August 2004 from three zones (principal fishing grounds for the species) in Chile’s southern channels (41°30′S–55°10′S). TL at which 50% of the individuals reach maturity was significantly different by sex, with females estimated to mature at 103.9 cm and males at 89.7 cm. The average estimated fecundity was 23.4 (SD 6.4) ova per female. We report on the relationships of clasper lengths and oviducal gland widths with TL and the stages of maturity. Length compositions were statistically different by sex in the same zone (P < 0.05) and between zones for combined sexes (P < 0.05). The proportion of females increased when these reached the TL at which 50% attained maturity, becoming highly available to the fishing gear, possibly in relation to the reproductive strategy. Finally, the results yielded valuable knowledge about population responses to exploitation through fishing.

The von Bertalanffy (vB) growth parameters for pink cusk-eel (Genypterus blacodes) were estimated for the Chilean australzone (41°28¢-57°00¢S) by gender and management fishing zones. A total of 47 026 samples were collected between March 1982 and May 2004, with total length ranging from 19 to 154 cm. Age determinations, based on the reading of saggital otoliths, were between 1 and 14 years in males and between 1 and 16 years in females. Statistical differences in growth were found between the sexes and management fishing zones. For the combined sexes the vB growth parameters for the northern-austral zone (41°28¢-47°00¢S) were: l ¥ ¼ 111.452 cm, k ¼ 0.186 year )1 , t 0 ¼ )0.912 year; and for the southern-austral zone (47°00¢-57°00¢S): l ¥ ¼ 123.447 cm, k ¼ 0.147 year )1 , t 0 ¼ )1.779 year.

We analyzed the allocation of effective fishing effort and the standardization of cardinalfish (Epigonus crassicaudus) catch rates in the multispecies demersal trawl fishery off central Chile. The period analyzed covered from 1997 to 2004 and included detailed information about fishing hauls. Each haul that contained cardinalfish was assigned into a particular fishing tactic (cluster) by using multivariate analysis of their catch composition. The catch rate standardization was carried out by generalized linear models (GLM). Three fishing tactics were discovered: the first directed effort at cardinalfish, the second at common hake (Merluccius gayi gayi), and the third at Patagonian grenadier (Macruronus magellanicus). Fishing tactic was used as an explanatory variable in the proposed GLM. The fishing tactic effect was one of the most important factors in explaining the variance in the GLM. These results are discussed in the context of how the assignation of a fishing tactic allows unbiased abundance indices to be obtained in this kind of multispecies demersal fishery.

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