TABLE 1.
Independent variables included in global Model Groups 1–4
| Independent variable | Categories/data range | Included in Model Group | |||
|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | ||
| Biotic variables | |||||
| Sex (f) | Female, Male. | y | — | y | — |
| Age‐class (f) | Adult, subadult, juvenile. NB. Juveniles excluded from Model Groups 3 and 4 | y | — | y | y |
| Body length (c) | 490–1,307 mm | y | y | y | y |
| Body condition (c) | 0.5–2 | y | y | y | y |
| Reproductive status (f) | Never reproduced, quiescent, pregnant or lactating. Term applicable to females only | — | y | — | y |
| Cause of death (f) | Sudden (n = 560), ill (n = 40), unknown (n = 10) | y | y | —* | —* |
| Biotic interactions | |||||
| Sex: Age, Sex: Body length, Sex: Body condition, Age: Body length, Age: Body condition, Body length: Body condition | y | — | y | — | |
| Reproductive status: Body condition, Reproductive status: Body length | — | — | — | y | |
| Abiotic variables | |||||
| Year (c) Month (c) | Month (Jan–Dec), fitted with circular spline, nested in Year | y | y | y | y |
| Year (c) | 1994–2010 | y | y | y | y |
| Region (f) | 8 regions (see Figure 5) | y | y | y | y |
| Distance from the coast (c) | Distance to coast, following river channel, 0–235 km). | y | y | y | y |
Factors (categories) and continuous variables are denoted (f) and (c), respectively. Model Groups 1 and 2: Dependent variable is presence/absence of an empty stomach. Model Groups 3 and 4: Dependent variable is the presence of each of 11 different prey types. Prey types were as follows: Eel, bullhead, cyprinid, salmonid, stickleback, crustacean, mammal, bird, insect, amphibian, and marine fish. Cause of death was not included in Model Groups 3 and 4 due to the vast majority of deaths being “sudden” in these reduced datasets (93.8% for Model Group 3, and 92.0% for Model Group 4). The link functions selected were as follows: probit for eel Model Group 3 and bullhead Model Group 4; cloglog for bullhead Model Group 3 and crustacean Model Group 4; logit for cyprinid Model Group 4; cauchit for all remaining models.