12 research outputs found
The function of sound production by Atlantic cod as inferred from patterns of variation in drumming muscle mass
Behaviour and orcadian rhythm of the fish bathygobius soporator Valenciennes (Gobiidae) under the influence of environmental salinity and temperature
Systematic bias in estimates of reproductive potential of an Atlantic cod (Gadus morhua) stock: implications for stock–recruit theory and management
Stock–recruit relationships that use spawning stock biomass (SSB) to represent reproductive potential assume
that the proportion of SSB composed of females and the relative fecundity (number of eggs produced per unit mass)
are both constant over time. To test these two assumptions, female-only spawner biomass (FSB) and total egg production
(TEP) were estimated for the Northeast Arctic stock of Atlantic cod (Gadus morhua) over a 56-year time period.
The proportion of females (FSB/SSB) varied between 24% and 68%, and the variation was systematic with length such
that SSB became more female-biased as the mean length of spawners increased. Relative fecundity of the stock
(TEP/SSB) varied between 115 and 355 eggs·g–1 and was significantly, positively correlated with mean length of
spawners. Both FSB and TEP gave a different interpretation of the recruitment response to reductions in stock size
(overcompensatory) compared with that obtained using SSB (either compensatory or depensatory). There was no difference
between SSB and FSB in the assessment of stock status; however, in recent years (1980–2001) TEP fell below
the threshold level at which recruitment becomes impaired more frequently than did SSB. This suggests that using SSB
as a measure of stock reproductive potential could lead to overly optimistic assessments of stock status
SPAWNING VOCALIZATIONS IN MALE FRESH-WATER GOBIIDS (PISCES, GOBIIDAE)
Males of two freshwater Italian gobies, the common goby, Padogobius martensii and the panzarolo goby, Knipowitschia punctatissima, emit trains of low-frequency pulses, i.e. 'drumming' sounds, in the presence of a ripe female in the nest. In P. martensii the drumming sound is usually followed by a tonal. sound (complex sound). Examination of the pulse structure suggests that these sounds are produced by muscles acting on the swimbladder. Both species exhibited high emission rates of spawning sounds, especially before the beginning of oviposition. Moreover, spawning sound production ceased only after the female abandoned the nest, which always occurred at the end of oviposition. This is the first study reporting the production among fishes of distinct sounds during protracted spawning. Unlike sounds produced just before mating by fishes with plank tonic or demersal zygotes, the spawning sound production of these gobies does not function to coordinate mating events in the nest. The presence of a two-part vocalization by male P. martensii even suggests a functional dichotomy of spawning sounds in this species