The silver roughy, Hoplostethus mediterraneus is a benthopelagic cosmopolitan fish regularly caught as by-catch of the deepwater
crustacean trawl fishery (CTF) in the central–eastern Mediterranean. Monthly samples of silver roughy were sampled
from the catches of four commercial trawlers in 2004. Each trawler operated in different fishing grounds (FGs), located off
Northern Tunisia, South of Sicily, Malta Islands and in South Levant, for which different exploitation levels are reported.
The overall length–frequency distribution (LFD) was constructed, and fishing impact indices (length as percentage of
LFD, optimum and maximum length, percentage of mega-spawners and total mortality/von Bertalanffy curvature ratio)
were calculated. In spite of an overall acceptable status (juveniles, matures and mega-spawners were present in the catch),
sampling data revealed significant differences in LFD shape and status indices between FGs. Those FGs traditionally considered
more exploited (Northern Tunisia and South of Sicily) showed a dominance of juveniles, a rarefaction of mega-spawners,
a reduction in maximum and asymptotic length and a higher Z/K ratio. Considering the general homogeneity of
Mediterranean deep-water habitats, the pelagic dispersal of eggs and the poor swimming capabilities of silver roughy, the
present results indicated that deep-water trawling may induce a slow and subtle, although significant, erosion of the older,
late maturing and slow growing component of the stocks in the Mediterranean (so-called longevity-overfishing).
[Show abstract][Hide abstract] ABSTRACT: The main objective of this study was fo know the age of silver roughy. A sample oj274 silver roughies Hoplostethus mediterraneus (Cuvier; /829) (pisces; Thachichthyidae) with a standard /ength (SL) ranging berween 36 and /76 mm was col1ected, Otoliths increments were interpreted by three difJèrl?nJ age readers. The maximum age was Il yeors in fema/es and 1Q years in ma/es. The differences (years) in age estimated by each age reader through statistica/ tests, showed no significant differences.
[Show abstract][Hide abstract] ABSTRACT: Overfishing is generally considered to be a reduction in biomass below some critical level such that the remaining fish are not able to replenish the population. We propose that the removal of large numbers of older age groups by fishing is also a form of overfishing, which we identify as longevity overfishing. Longevity overfishing is a potentially important consideration for the commercial fisheries off Canada’s Pacific coast that are dominated by species that have maximum ages of 30 years or longer. Sablefish is one of the key long-lived species that is managed for biomass and not longevity. An age structured model showed that if younger fish do not have the same productivity per unit biomass as older fish, the population depleted of older fishes would not recover after a shift of carrying capacity from a prolonged period of poor productivity to a more productive ocean ecosystem. Current management of long-lived species implicitly assumes that young fish will have the same productivity as older fishes, an assumption that is not supported by a sparse literature, and is thus not precautionary. We propose that the evolved age structure is an indication that long-lived species must be managed for longevity as well as biomass, which requires a management time frame that is decades and not annual.
Progress In Oceanography 02/2006; 68(2):289-302. DOI:10.1016/j.pocean.2006.02.005 · 3.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Age determination and validation studies on deep-water marine fishes indicate they are difficult to age and often long-lived. Techniques for the determination of age in individual fish includes growth-zone analysis of vertebral centra, fin rays and spines, other skeletal structures, and otoliths (there are three sets of otoliths in most bony fish semicircular canals, each of which is made of calcium carbonate). Most have regular increments deposited as the fish (and its semicircular canals) grows. The most commonly used otolith for age determination is the largest one called the sagitta. Age validation techniques include: (1) tag-recapture, often combined with oxytetracycline injection and analysis in growth-zones of bone upon recapture; (2) analysis of growth-zones over time; and (3) radiometric approaches utilizing a known radioactive decay series as an independent chronometer in otoliths from bony fishes. We briefly summarize previous studies using these three validation approaches and present results from several of our radiometric studies on deep-water, bony fishes recently subjected to expanding fisheries. Radiometric age validation results are presented for four species of scorpaenid fishes (the bank, Sebastes rufus, and bocaccio, S. paucispinis, rockfishes, and two thornyhead species, Sebastolobus altivelis and S. alascanus). In addition, our analysis of scorpaenids indicates that longevity increases exponentially with maximum depth of occurrence. The reason that the deep-water forms of scorpaenid fishes are long-lived is uncertain. Their longevity, however, may be related to altered physiological processes relative to environmental parameters like low temperature, high pressures, low light levels, low oxygen, and poor food resources.
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