Mesopelagic fish derivatives in the southern Benguela upwelling region

234

177

We examined data on size of dominant demersal fish species in the SE Atlantic (44 species) and the NW Mediterranean (31 species) to determine whether there is a general tendency to increasing size towards deeper waters. Our results demonstrate significant positive size-depth relationships for most species examined (63 % SE Atlantic and 74 % NW Mediterranean). The relationships examined involved both a tendency towards greater size with ~ncreasing depth and a tendency towards smaller size towards shallower bottoms. The average ( * standard error) rate of increase in fish length with increasing depth was found to be 0.09 f 0.01 cm length (m depth)-' for the SE Atlantic species and 0.06 k 0.007 cm length (m depth)-' for the NW Mediterranean species. In addition, we found the slope and intercept of these relationships to scale approximately to the 3/4 power of the maximum and minimum fish size respectively, showing that interspecific differences in the nature of this relationship depend on the size range of the different species. Consideration of several hypotheses to account for this general pattern suggests that it reflects a migratory (or diffusive) movement towards deeper waters during ontogeny, where fish benefit from the extended Lives and lower metabolism at lower temperatures. We suggest this pattern is evolutionary In nature, and due to inherited behaviour.

Section: Discussionmentioning

confidence: 82%

Bathymetric trends in demersal fish size: is there a general relationship?

Macpherson¹,

Duarte²

1991

234

177

“…These species spawn throughout the year, with peaks in late winter through spring (Young et al 1987, Armstrong & Prosch 1991, Prosch 1991. The spawning populations are confined to the continental slope in the vicinity of landmasses (Robertson 1976, Hulley & Prosch 1987. However, there is some controversy in the literature about the relationship between spawning and upwelling.…”

Section: Introductionmentioning

confidence: 99%

Spring spawning and early nursery zone of the mesopelagic fish Maurolicus parvipinnis at the coastal upwelling zone off Talcahuano, central Chile

Landaeta¹,

Castro²

2002

Coastal upwelling areas along eastern boundary currents have been recognized for having high planktonic production. In the Humboldt Current System off South America, little is known about the reproductive strategies of mesopelagic fishes and their utilization of highly productive coastal upwelling areas for spawning and early development. In the present study, we first document the spawning and nursery area of the highly abundant mesopelagic fish Maurolicus parvipinnis in the coastal upwelling zone off Talcahuano, central Chile. Second, we propose a mechanism by which ontogenetic and diel changes in vertical distribution of the early life history stages and the utilization of the local hydrodynamics facilitates the development of the larvae of this species over the shelf and nearby slope in a highly productive environment. Our results show that M. parvipinnis spawn during early spring at mid-depth in zones of intense upwelling. Larvae hatch mostly in the spawning area located on the southern edge of the slope, and are then advected northwards along the slope or over the shelf where high larval food concentrations occur. Over the shelf, larger larvae tend to vertically migrate, spending part of the night hours in the shallower layer where the water temperature is higher, and where food is most abundant. During the day, they remain at depth where offshore transport may be decreased. Those larvae that are not retained over the shelf are advected offshore, probably in the surface Ekman layer or in association with cold filaments that usually develop off the central zone along the shelf off Talcahuano. Although information on the spawning strategy of other Maurolicus species worldwide is sparse, there are some similarities in relation to the subsurface spawning, the larval presence in nearshore waters, and the early spring spawning season in association with periods of increased food availability. The spawning strategy described herein, therefore, may be a more common feature than previously believed for Maurolicus species, especially along coastal upwelling areas in eastern boundary currents.

“…By avoiding shallow foraging predators (Staby 2010), they increase the likelihood of survival and thus future reproductive output during the next spawning season (Giske & Aksnes 1992, Ros land & Giske 1994, 1997. This change in behaviour implies that adult fish are able to survive at depth through feeding on deep distributed prey in daytime (Giske et al 1990, Bagøien et al 2001 and/or by using lipid reserves (Falk-Petersen et al 1986, Hulley & Prosch 1987. The proportion of overwintering adults feeding in daytime and the number of prey ingested (mainly overwintering copepods) are probably relatively low (Bagøien et al 2001, Srisomwong 2009), with feeding rates at best sufficient to maintain zero growth (Giske & Aksnes 1992, Rosland & Giske 1997.…”

Section: Non-migrating Individualsmentioning

confidence: 99%

Long-term acoustical observations of the mesopelagic fish Maurolicus muelleri reveal novel and varied vertical migration patterns

Staby¹,

Røstad²,

Kaartvedt³

2011

We studied the temporal dynamics in the vertical distribution of Maurolicus muelleri scattering layers (SL) by examining continuous acoustic recordings over a 15 mo period in Masfjorden, Norway, complemented by intermittent sampling campaigns. The data revealed known patterns as normal diel vertical migration (DVM), midnight sinking between dusk and dawn, and periods without migrations, as well as novel behaviours consisting of early morning ascents, reverse diel vertical migrations, and interrupted ascents in the evening. During the first autumn of the study, adult fish modified their normal DVM behaviour by suspending their migration in the evening, yet ascending toward the surface in the later part of the night to reach upper layers during dawn. This behaviour was not observed during the second autumn of the study. By mid-to end of November (1st autumn), adult fish had suspended the nocturnal ascent entirely, and in the subsequent period until the end of January, a fraction of the population rather performed limited reverse migrations, slightly shifting their vertical distribution upwards during the first part of the day. From January to March 2008, fish interrupted their evening ascent at apparently random intervals and returned to deeper waters, instead of completing a full ascent to the surface. Our study underlines the value of long-term recordings, with the results suggesting that M. muelleri has the capability of changing its behaviour in response to ontogeny and internal state (satiation and hunger) as well as to external stimuli. KEY WORDS: Diel vertical migration · DVM · Scattering layers · Maurolicus muelleri · Ontogeny · Stationary hydroacoustics Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 441: [241][242][243][244][245][246][247][248][249][250][251][252][253][254][255] 2011 from the surface (Neilson & Perry 1990, Baliño & Aksnes 1993, Widder & Frank 2001, Cohen & Forward 2009, Staby & Aksnes 2011.Several hypotheses for vertical migrations on a population level have been put forward. Eggers (1978) proposed that the adaptive value of vertical migrations was to minimise predation risk by avoiding predators. The predator avoidance hypothesis was later extended to include the optimisation of foraging in the anti-predation window at intermediate light intensities at dusk and dawn (Clark & Levy 1988, Scheuerell & Schindler 2003. The bioenergetic efficiency hypothesis states that organisms distribute at temperatures which maximise growth (Wurtsbaugh & Neverman 1988, Giske & Aksnes 1992, Bevelhimer & Adams 1993, while the foragingopportunity hypothesis predicts that the depth distribution of the predator overlaps with depth changes of its prey (Levy 1990a, Neilson & Perry 1990. On an individual level, the hunger-satiation hypothesis assumes that vertical movements of individuals are triggered by a change in their hunger or satiation state (Pearre 2003).Mueller's pearlside Maurolicus muelleri Gmelin 1789, a small mesopelagic fish (standard le...