Increases in the relative abundance of mid-trophic level fishes concurrent with declines in apex predators in the subtropical North Pacific, 1996–2006

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.

[1]  C. Boggs,et al.  Hawaii's Pelagic Fisheries , 1993 .

[2]  M. Musyl,et al.  Pelagic longline gear depth and shoaling , 2006 .

[3]  Daniel E. Schindler,et al.  The Role of Sharks and Longline Fisheries in a Pelagic Ecosystem of the Central Pacific , 2002, Ecosystems.

[4]  M. Maunder,et al.  Biomass, Size, and Trophic Status of Top Predators in the Pacific Ocean , 2006, Science.

[5]  Steven J. D. Martell,et al.  Reconstructing ecosystem dynamics in the central Pacific Ocean, 1952-1998. II. A preliminary assessment of the trophic impacts of fishing and effects on tuna dynamics , 2002 .

[6]  P. Ward,et al.  Inferring the depth distribution of catchability for pelagic fishes and correcting for variations in the depth of longline fishing gear , 2005 .

[7]  B. Worm,et al.  META-ANALYSIS OF COD-SHRIMP INTERACTIONS REVEALS TOP-DOWN CONTROL IN OCEANIC FOOD WEBS , 2003 .

[8]  Fishery Bulletin , 2022 .

[9]  I. Nakamura,et al.  FAO species catalogue. v. 15: snake mackerels and cutlassfishes of the world (families Gempylidae and Trichiuridae). An annotated and illustrated catalogue of the Snake Mackerels, Snoeks, Escolars, Gemfishes, Sackfishes, Domine, Oilfish, Cutlassfishes, Scabbardfishes, Hairtails and Frostfishes known , 1993 .

[10]  Ransom A. Myers,et al.  SHIFTS IN OPEN‐OCEAN FISH COMMUNITIES COINCIDING WITH THE COMMENCEMENT OF COMMERCIAL FISHING , 2005 .

[11]  Jae S. Choi,et al.  Trophic Cascades in a Formerly Cod-Dominated Ecosystem , 2005, Science.

[12]  Melanie Abecassis,et al.  Ocean's least productive waters are expanding , 2008 .

[13]  C. Walters,et al.  Keystone predators in the Central Pacific , 1999 .

[14]  T. Essington,et al.  Fishing through marine food webs. , 2006, Proceedings of the National Academy of Sciences of the United States of America.

[15]  George L. Pickard,et al.  Descriptive Physical Oceanography: An Introduction , 1963 .