Food habits of an endangered seabird indicate recent poor forage fish availability off western South Africa

Crawford, Robert J. M.; Sydeman, William J.; Thompson, Sarah; Sherley, Richard B.; Makhado, Azwianewi B.

doi:10.1093/icesjms/fsz081

Cited by 19 publications

(26 citation statements)

References 48 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This includes studies on the take of (a) age‐0 cod (Gadidae) by puffins in the GoA (Hatch & Sanger, ), (b) age‐0 rockfish ( Sebastes spp.) by murres in the central California Current (Mills et al, ), (c) age‐0 and age‐1+ Pacific sand lance (PSL; Ammodytes personatus ) and capelin ( Mallotus catervarius ) by puffins in the GoA and Aleutian archipelago (Piatt et al, ), and (d) age‐0 and older anchovy ( Engraulis encrasicolus ) and sardine ( Sardinops sagax ) by Cape gannets ( Morus capensis ) in the southern Benguela ecosystem (Crawford, Sydeman, Thompson, Sherley, & Makhado, ). We therefore assume that sampling in proportion to abundance also occurred in this study.…”

Section: Introductionmentioning

confidence: 99%

Effects of ocean climate on the length and condition of forage fish in the Gulf of Alaska

Thompson

García‐Reyes

Sydeman

et al. 2019

Fisheries Oceanography

Self Cite

View full text Add to dashboard Cite

Climatic drivers of the size and body condition of forage fish in the North Pacific are poorly known. We hypothesized that length and condition of forage fish in the Gulf of Alaska (GoA) vary in relation to ocean temperature on multiple scales. To test this hypothesis, we analyzed morphometric data for capelin (Mallotus catervarius) and Pacific sand lance (PSL; Ammodytes personatus) sampled by a seabird (Cerorhinca monocerata) in two regions of the GoA, 1993–2016. Based on previous studies, we predicted that capelin length and body condition (Fulton's K) would be negatively related to the Pacific Decadal Oscillation (PDO) and sea surface temperature (SST), whereas PSL length and condition would be positively related. Interannual variation in length and body condition was evaluated relative to seasonal values of ocean climate using regression. Forage fish length and condition varied interannually, between sampling regions, and were dependent on the size/age class of the fish sampled. As predicted, length and body condition of capelin (mostly age 1+) were negatively related to the PDO and SST. Relationships with ocean climate for PSL varied by size/age class: positive for putative age‐0 fish and negative for putative age‐1+ fish. We conclude that our hypothesis was supported for capelin and partially supported for PSL. This study demonstrates that ocean climate determines key morphometric characteristics of forage fish that may relate to interannual variation in the energetic value of prey, and provides an example of how seabirds can be used to obtain specimens for evaluations of potential prey quality.

show abstract

Section: Introductionmentioning

confidence: 99%

Effects of ocean climate on the length and condition of forage fish in the Gulf of Alaska

Thompson

García‐Reyes

Sydeman

et al. 2019

Fisheries Oceanography

Self Cite

View full text Add to dashboard Cite

show abstract

“…This decline also coincided with an eastward displacement of a number of marine resources in South Africa (Blamey et al, 2015), including spawning adults of sardine and anchovy (Coetzee, van der Lingen, Hutchings, & Fairweather, 2008;Roy, van der Lingen, Coetzee, & Lutjeharms, 2007). These environmental changes combined with fishing pressure (Coetzee et al, 2008;Mhlongo, Yemane, Hendricks, & van der Lingen, 2015) to lower the availability of prey for seabirds breeding to the north of Cape Town (Crawford, Sydeman, Thompson, Sherley, & Makhado, 2019).…”

Section: Discussionmentioning

confidence: 97%

“…A lack of suitable prey, predominantly small pelagic fish, is believed to be the main driver for declines in African penguin numbers in South Africa over the last three decades (Crawford et al, 2011(Crawford et al, , 2019Crawford, Sabarros, Fairweather, Underhill, & Wolfaardt, 2008;Sherley et al, 2017), with sporadic oiling events, habitat destruction, disturbance, and predation also contributing to the losses (Crawford et al, 2000;Makhado, Crawford, Waller, & Underhill, 2013;Pichegru, 2012;Weller et al, 2014). In 2013, the South African government put in place a Biodiversity Management Plan (BMP) for the African penguin (DEA, 2013).…”

Section: Discussionmentioning

confidence: 99%

The conservation status and population decline of the African penguin deconstructed in space and time

Sherley

Crawford²,

Blocq³

et al. 2020

Ecology and Evolution

View full text Add to dashboard Cite

show abstract

“…(2011) identified a threshold of approximately one‐third of maximum prey biomass below which seabird breeding success was consistently reduced and more variable. Similarly, when the biomass of sardine spawners fell below c. 25% of its maximum observed value, survival of adult African penguins ( Spheniscus demersus , Spheniscidae) decreased markedly (Robinson et al., 2015) and survival and numbers breeding decreased for three Benguela seabirds when a forage availability index reached low values (Crawford et al., 2019). There may be a still lower ecological threshold (15%–18% according to our study) where prey species, or at least spatial components of prey stocks (e.g.…”

Section: Discussionmentioning

confidence: 99%

Seabird‐induced natural mortality of forage fish varies with fish abundance: Evidence from five ecosystems

et al. 2020

Self Cite

View full text Add to dashboard Cite

Forage fish populations often undergo large and rapid fluctuations in abundance. However, most of their predators are buffered against such fluctuations owing to their slower pace of life, which allows them to maintain more stable populations, at least during short periods of food scarcity. In this study, we investigated top-down processes exerted by seabirds on forage fish stocks in five contrasted marine ecosystems, compiling numerous datasets on seabird counts, diets, energetic needs and prey energy content and abundance. Off Norway, South Africa, Peru, Sweden and Scotland, we found that predation pressure-estimated as the proportion of a fish stock consumed by seabirds-was generally low (median = 1%), but increased sharply at low levels of prey abundance. When prey biomass decreased below 15 to 18% of its maximum recorded value, predation by seabirds became a source of important additional pressure on prey stocks (~20% of prey biomass is consumed by seabirds). An earlier empirical study advocated for keeping forage stocks from falling below a threshold of 33% of long-term maximum prey biomass in order to safeguard seabird breeding success, but here we further suggest that a threshold of 18% should be considered as a limit not to be exceeded for the sake of the forage fish themselves, and below which extra cautious management of fisheries may be required. Nevertheless, despite exceptionally high rates of predation on some occasions, predation pressure was not correlated with prey dynamics, suggesting an absence of prey entrapment due to seabirds alone in these five ecosystems.

show abstract

Food habits of an endangered seabird indicate recent poor forage fish availability off western South Africa

Cited by 19 publications

References 48 publications

Effects of ocean climate on the length and condition of forage fish in the Gulf of Alaska

Effects of ocean climate on the length and condition of forage fish in the Gulf of Alaska

The conservation status and population decline of the African penguin deconstructed in space and time

Seabird‐induced natural mortality of forage fish varies with fish abundance: Evidence from five ecosystems

Contact Info

Product

Resources

About