{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,4]],"date-time":"2025-11-04T15:50:17Z","timestamp":1762271417427},"reference-count":34,"publisher":"Oxford University Press (OUP)","issue":"5","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2010,7,1]]},"abstract":"<jats:title>Abstract<\/jats:title>\n               <jats:p>Vaz Velho, F., Barros, P., and Axelsen, B. E. 2010. Day\u2013night differences in Cunene horse mackerel (Trachurus trecae) acoustic relative densities off Angola. \u2013 ICES Journal of Marine Science, 67: 1004\u20131009. The assessment and the management of the Cunene horse mackerel in Angola rely heavily on abundance estimates from hydroacoustic surveys. Acoustic data collected from 1994 to 1999 were analysed to quantify diurnal variation in relative acoustic densities at 38 kHz. The nautical-area scattering coefficient (sA, m2 nautical mile\u22122) was characterized by clear day\u2013night differences: sA values recorded during the day were significantly higher (mean sA: 135 m2 nautical mile\u22122) than the corresponding night-time values (mean sA 83 m2 nautical mile\u22122). This pattern is associated with differences in behaviour and horizontal and vertical distributions between day and night: by day, the fish school near the seabed, and by night, they move into the pelagic zone and disperse into widespread scattering layers. More than 40% of the total backscatter by day originated from the bottom 10 m, but at night this proportion decreased to &lt;10%. The findings demonstrate considerable influences of behaviour and aggregation dynamics on acoustic measurements. Possible implications for the estimates of acoustic abundance are discussed in the light of the differences.<\/jats:p>","DOI":"10.1093\/icesjms\/fsq004","type":"journal-article","created":{"date-parts":[[2010,3,12]],"date-time":"2010-03-12T20:49:11Z","timestamp":1268426951000},"page":"1004-1009","source":"Crossref","is-referenced-by-count":5,"title":["Day\u2013night differences in Cunene horse mackerel (Trachurus trecae) acoustic relative densities off Angola"],"prefix":"10.1093","volume":"67","author":[{"given":"Filomena","family":"Vaz Velho","sequence":"first","affiliation":[{"name":"Instituto Nacional de Investiga\u00e7\u00e3o Pesqueira, Minist\u00e9rio das Pescas de Angola, Ilha de Luanda, CP 2601, Luanda, Angola"}]},{"given":"Pedro","family":"Barros","sequence":"additional","affiliation":[{"name":"Campus de Gambelas, University of Algarve, 8005-139 Faro, Portugal, and FAO, Viale delle Terme di Caracala, 00153 Roma, Italy"}]},{"given":"Bj\u00f8rn Erik","family":"Axelsen","sequence":"additional","affiliation":[{"name":"Institute of Marine Research, PO Box 1870 Nordnes, 5817 Bergen, Norway"}]}],"member":"286","published-online":{"date-parts":[[2010,3,12]]},"reference":[{"key":"2019081212164971800_FSQ004C1","first-page":"45","article-title":"Report on Survey Errors Workshop, Cape Town, South Africa, 4\u20137 December 2000","author":"Anon.","year":"2003"},{"key":"2019081212164971800_FSQ004C2","first-page":"31","article-title":"Report on Survey Errors Workshop, Cape Town, South Africa, 14\u201315 December 2003","author":"Anon.","year":"2004"},{"key":"2019081212164971800_FSQ004C3","article-title":"Surveys of the pelagic resources, 7 July\u201320 August 2007","author":"Anon.","year":"2007"},{"key":"2019081212164971800_FSQ004C4","first-page":"40 pp. + Papers and Annex 115","article-title":"Acoustic identification and abundance estimation of horse mackerel, jellyfish and mesozooplankton in the Benguela 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