Forty Years of Winter: Cetaceans Observed During the Southbound Migration of Gray Whales, Eschrichtius robustus, Near Granite Canyon, Central California

From December to February in most years from 1967 to 2007, observers counted gray whales, Eschrichtius robustus, from shore sites south of Carmel in central California. In addition to gray whales, other cetacean species were also recorded. These observations were summarized and compared among survey platforms and to ocean conditions. Eleven cetacean species were identified including eight odontocete species (killer whale, Orcinus orca; Pacific white-sided dolphin, Lagenorhynchus obliquidens; common dolphin, Delphinus spp.; bottlenose dolphin, Tursiops truncatus, northern right whale dolphin, Lissodelphis borealis; Risso’s dolphin, Grampus griseus; Dall’s porpoise, Phocoenoides dalli; and harbor porpoise, Phocoena phocoena) and three mysticete species (humpback whale, Megaptera novaeangliae; minke whale, Balaenoptera acutorostrata; and blue whale, Balaenoptera musculus). As expected, the detection of certain species among survey platforms (shore-based census watches, 25-power “Big Eye” binocular watches, and aerial surveys) was limited by species surfacing behavior and/or bathymetric preference. Comparisons among the shore-based census efforts showed a significant difference in sightings rates from 1967–84 (n = 14, mean = 0.11, SD = 0.11) to 1985–2007 (n = 11, mean = 1.48, SD = 0.47; t-Test: p < 0.001, df = 23). The warm period observed during the 1990’s may partially explain the increase in sighting rates and diversity of species observed at the census site compared to the much cooler temperatures of the 1970’s.

Croissance et détermination de l'âge par lecture d'écailles d'un poisson plat de Côte d'Ivoire, Cynoglossus canariensis (Steind. 1882)

Cynoglossus canariensis has a very rapid growth. The rate of the males is 0,36 and the female one is 0,32. The asymptotic size is 55,0cm for the females and 50,5cm for the males. Females and males younger than three years (40cm), which represent 90 per cent of the Côte d'Ivoire stock have a similar growth, so the average equation: Lt=53,5 (1-e -0,34(t+1)) will be used.

The potential use of time-area closures to reduce catches of bigeye tuna (Thunnus obesus) in the purse-seine fishery of the eastern Pacific Ocean

Skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares), and bigeye (Thunnus obesus) tunas are caught by purse-seine vessels in the eastern Pacific Ocean (EPO). Although there is no evidence to indicate that current levels of fishing-induced mortality will affect the sustainability of skipjack or yellowfin tunas, fishing mortality on juvenile (younger than 5 years of age) bigeye tuna has increased, and overall fishing mortality is greater than that necessary to produce the maximum sustainable yield of this species. We investigated whether time-area closures have the potential to reduce purse-seine bigeye catches without significantly reducing skipjack catches. Using catch and effort data for 1995–2002, we identified regions where the ratio of bigeye to skipjack tuna catches was high and applied simple closed-area models to investigate the possible benefits of time-area closures. We estimated that the most optimistic and operationally feasible 3-month closures, covering the equatorial region of the EPO during the third quarter of the year, could reduce bigeye catches by 11.5%, while reducing skipjack tuna catches by 4.3%. Because this level of bigeye tuna catch reduction is insufficient to address sustainability concerns, and larger and longer closures would reduce catches of this species signficantly, we recommend that future research be directed toward gear technology solutions because these have been successful in many other fisheries. In particular, because over 50% of purse-seine catches of bigeye tuna are taken in sets in which bigeye tuna are the dominant species, methods to allow the determination of the species composition of aggregations around floating objects may be important.

Sablefish, Anoplopoma fimbria, Populations on Gulf of Alaska Seamounts

Sablefish, Anoplopoma fimbria, were tagged and released on Gulf of Alaska seamounts during 1999–2002 to determine the extent, if any, of emigration from the seamounts back to the continental slope and of movement between seamounts. Seventeen sablefish from Gulf of Alaska seamounts have been recovered on the continental slope since tagging began, verifying that seamount to slope migration occurs. Forty-two sablefish were recovered on the same seamounts where they were tagged, and none have been recaptured on seamounts other than the ones where they were released. Sablefish populations on Gulf of Alaska seamounts are made up of individuals mostly older than 5 years and are maledominant, with sex ratios varying from 4:1 up to 10:1 males to females. Males are smaller than females, but the average age of males is greater than that of females, and males have a greater range of age (4–64 yr) than females (4–48 yr). Otoliths of seamount fish frequently have an area of highly compressed annuli, known as the transition zone, where growth has suddenly and greatly slowed or even stopped. Because transition zones can be present in both younger and older seamount fish and are rare in slope fish, formation of otolith transition zones may be related to travel to the seamounts. The route sablefish use to reach the seamounts is so far unknown. One possibility is that fish enter the eastward-flowing North Pacific Current off the Aleutian Islands or western Gulf of Alaska and travel more or less passively on the current until encountering a seamount. The route from seamount back to slope would likely be the northwardflowing Alaska Current. These routes are discussed in light of tag recovery locations of slope- and seamount-tagged fish.