|
Increases in the relative abundance of mid-trophic level fishes concurrent with
declines in apex predators in the subtropical North Pacific, 1996–2006 |
| |
|
Polovina, J.J., Abecassis, M., Howell, E.A., Woodworth, P. |
| |
| Abstract:
Catch rates for the 13 most abundant species caught in the
deep-set Hawaii-based longline fishery over the past decade
(1996–2006) provide evidence of a change among the top North
Pacific subtropical predators. Catch rates for apex predators
such as blue shark (Prionace glauca), bigeye (Thunnus obesus)
and albacore (Thunnus alalunga) tunas, shortbill spearfish
(Tetrapturus angustirostris), and striped marlin (Tetrapturus
audax) declined by 3% to 9% per year and catch rates for four
midtrophic species, mahimahi (Coryphaena hippurus), sickle
pomfret (Taractichthys steindachneri), escolar (Lepidocybium
flavobrunneum), and snake mackerel (Gempylus serpens), increased
by 6% to 18% per year. The mean trophic level of the catch for
these 13 species declined 5%, from 3.85 to 3.66. A shift in the
ecosystem to an increase in midtrophic-level, fast-growing and
short-lived species is indicated by the decline in apex predators
in the catch (from 70% to 40%) and the increase in species with
production to biomass values of 1.0 or larger in the catch (from
20% to 40%).
This altered ecosystem may exhibit more temporal variation in
response to climate variability.
|
|