The need to combine with ancillary data to interpret the
results
Our approach is not self-sufficient and relies partly on the
availability of expert and/or literature knowledge to interpret the
spatial patterns identified through EOF as ecological processes. EOF
capture the main modes of variation of the spatio-temporal fields.
Combining those results with ancillary data and knowledge about the
timing of the main phenological events is needed to interpret the
results.
Typically, for sole, some studies investigating the timing and the
spatial distribution of egg and larvae distribution have been used to
corroborate our interpretation of EOF (Arbault et al., 1986; Petitgas,
1997). For hake, survey data have recorded mature individuals during the
spawning season (Alvarez et al., 2004) and catch declarations data have
been used to evidence reproduction migration at the level of rough
statistical rectangles (Poulard, 2001). They were proven to be
consistent with our analysis too.
Still, those data are limited. In both cases, the data were restricted
to few samples from very old spring surveys and they have not been
updated since this period. Furthermore, in many other cases there might
not be any reference data to corroborate the EOF results. One should
encourage to increase the quantity of available data by conducting new
surveys to obtain direct observations of spawning areas (Fox et al.,
2008). However, this requires important investments and depends on the
ability of institutions and government to raise funds for these surveys.
Alternatively, expert knowledge of fishermen could be a valuable
complement to interpret the main modes of variation (Yochum et al.,
2011) when other data are missing. Bezerra et al. (2021) and Silvano et
al. (2006) proved the usefulness of fishermen knowledge to determine the
temporality of fish spawning and to identify some spawning grounds by
crossing the information of aggregation areas provided by several
fishermen.