Geology topics

William Walker

Publications and source records attributed to William Walker.

4 recordsLinked to original sources

USGS2016

Food of Flesh-footed shearwaters Puffinus carneipes associated with high-seas driftnets in the central North Pacific Ocean

We examined digestive tract contents and stable nitrogen isotope ratios in breast muscles of Flesh-footed Shearwaters Puffinus carneipes associated with high-seas driftnet fisheries in the central North Pacific Ocean. Small fish, Lanternfish (Myctophidae) and Pacific Saury Cololabis saira , were the principal prey found in the digestive tracts. Pieces of unidentified fish, possibly Pacific Pomfret Brama japonica , and shredded squid tissue, mostly Neon Flying Squid Ommastrephes bartrami , in the digestive tracts indicate scavenging at driftnet fishing operations. Although soft-bodied animals such as Velella sp. were rare in the digestive tracts, low stable nitrogen isotope values (δ 15 N) suggest Flesh-footed Shearwaters feed heavily on such low trophic level animals.

Emu↗

USGS2000

Foods, trophic relationships, and migration of Sooty and Short-tailed Shearwaters associated with squid and large-mesh driftnet fisheries in the North Pacific Ocean

We salvaged dead birds from high seas driftnets in the Central North Pacific Ocean during a study of the impact of high seas driftnet fishing on marine ecosystems. Digestive tract contents and stable isotopes of nitrogen and carbon in breast muscles of these birds were analyzed to assess the effect of driftnets on the trophic relationships of marine birds. The diets of Sooty ( Puffinus griseus ) and Short-tailed ( P. tenuirostris ) Shearwaters associated with high seas driftnets in the transitional region of the North Pacific Ocean overlap broadly. The principal differences between them include 1) Sooties prey more heavily on immature stages of invertebrates, especially the barnacle Lepas fascicularis than do Short-tails, 2) Pacific saury ( Cololabis saira ) are the primary fish taken by Sooties while lanternfish ( Myctophidae ) are the primary fish taken by Short-tails, and 3) Sooties take a wider variety of prey than do Short-tails. During the last years of extensive high seas driftnet fishing (early 1990's), both shearwaters augmented their diets with about 15% offal and discards from fishing vessels. Values for stable isotopes of nitrogen and carbon in breast muscle tissues (δ 15 N and δ 15 C) indicate the extent and timing of movements of Sooty Shearwaters: including arrival of migrants from the south Pacific (April-May), east to west movement from the eastern Pacific (May-June), and west to east movement from Japan (August-September). Fall migrant Sooties were not detected. The only movements of Short-tails that we detected were a few south-bound migrants in September-November.

Waterbirds↗

USGS1997

Trophic relationships of albatrosses associated with squid and large-mesh drift-net fisheries in the North Pacific Ocean

The diets of Laysan ( Diomedea immutabilis ) and black-footed albatrosses ( D . nigripes ) killed in squid and large-mesh drift nets in the transitional zone of the North Pacific Ocean were investigated by examining the contents of the digestive tracts and determining δ 13 C and δ 15 N values in breast-muscle tissue. The results show that ( i ) the combined prey of the two species of albatross consists of over 46 species of marine organisms including coelenterates, arthropods, mollusks, fish, and marine mammals; ( ii ) both species supplement their traditional diets with food made available by commercial fishing operations (e.g., net-caught squid and offal); ( iii ) while obtained from drift nets, diets of nonbreeding Laysan and black-footed albatrosses are dominated by neon flying squid ( Ommastrephes bartrami ); ( iv ) in the absence of drift-net-related food, Laysan albatrosses feed most heavily on fish and black-footed albatrosses feed most heavily on squid; and ( v ) based on δ 15 N values, nonbreeding adult Laysan albatrosses from the transitional zone of the North Pacific Ocean and Laysan albatross nestlings fed by adults from Midway Island in the subtropical Pacific feed at one trophic level and one-third of a trophic level lower than black-footed albatrosses, respectively.

Canadian Journal of Zoology↗

USGS1997

Foods of northern fulmars associated with high-seas drift nets in the transitional region of the North Pacific

We examined digestive tract contents and nitrogen stable isotope ratios in breast muscles of northern fulmars ( Fulmarus glacialis ) salvaged from squid and large-mesh drift nets in the transitional North Pacific. Lantern fishes (Myctophidae) were the principal prey item found in the digestive tracts. Pieces of unidentified fishes (probably Pacific pomfret Brama japonica ) and shredded squid tissue (probably neon flying squid Ommastrephes bartrami ) indicate scavenging at fishing operations. Although soft-bodied prey such as Velella were not found in the digestive tracts, δ 15 N values suggest that fulmars may feed heavily on such low trophic-level animals.

Northwestern Naturalist↗