Since kleptoparasitism, that is, stealing food from other entities that have procured that food earlier for themselves, is a widespread strategy in animals, it is no surprise that birds also engage in this kind of behavior (up to 856 accounts of some sort of interspecific thievery). Food stealing skills is even related to parental quality in Sterna dougallii. Honest parents had lower productivity. Additionally, in parrot-owner behavioral problems dynamics, stealing human food got a 2.34 in a 5-point Likert scale where 5 = always.
On top of that, theoretical ecology tells us that behavioral dynamics are characterized by a cooperation/conflict tension where a behavior such as theft may thrive (while also depending on many other factors, e.g.: larger thieves tended to get the highest payoff, and bear in mind size is but one factor). So I think a bird will maximize stealing if the opportunity is present to it and whether it's physically capable of doing it.
In Larus argentatus, head turns, approaches, and angular body position were three behavioral markers identified in an ethogram to measure attention to anthropogenic food-based contexts. I think this article is the one that is key to your question, considering how difficult it is to find statistics for how often thievery from anthropogenic sources happens. It is key, because combined with theoretical ecology, and the amount of bird intelligence research nowadays, it shows intuitively that birds will probably steal from human fish traps 1) if they have knowledge about it, and 2) as much as they can.
Anecdotally, birds, (both known and unknown to me) have also stolen from me several times in varied environments (many of them could be considered "traps" or at least "food containers that require a certain degree of skill to operate or get to"), but not fish traps.
Anne Tygesen & Björn Forkman (2023) The Parrot–Owner Relationship and Problem Behaviors in Parrots, Anthrozoös, DOI: 10.1080/08927936.2023.2238434
David A. Shealer, Jeffrey A. Spendelow, Jeff S. Hatfield, Ian C. T. Nisbet, The adaptive significance of stealing in a marine bird and its relationship to parental quality, Behavioral Ecology, Volume 16, Issue 2, Mar./Apr. 2005, Pages 371–376, https://doi.org/10.1093/beheco/ari008
Feist F, Graham P. An ethogram identifies behavioural markers of attention to humans in European herring gulls (Larus argentatus). Biol Open. 2023 Jun 15;12(6):bio060016. doi: 10.1242/bio.060016. Epub 2023 Jun 13. PMID: 37309817; PMCID: PMC10281265.
Hadjichrysanthou C, Broom M, Rychtář J. Models of kleptoparasitism on networks: the effect of population structure on food stealing behaviour. J Math Biol. 2018 May;76(6):1465-1488. doi: 10.1007/s00285-017-1177-7. Epub 2017 Sep 18. PMID: 28921258; PMCID: PMC5840298.
Morand-Ferron J, Sol D. and Lefebvre L (2007) Food stealing in birds: brain or brawn? Animal Behaviour, 74, 6, 1725-1734. https://doi.org/10.1016/j.anbehav.2007.04.031
Phillips JA, Peacock SJ, Bateman A, Bartlett M, Lewis MA, Krkošek M. An asymmetric producer-scrounger game: body size and the social foraging behavior of coho salmon. Theor Ecol. 2018;11(4):417-431. doi: 10.1007/s12080-018-0375-2. Epub 2018 May 1. PMID: 30931016; PMCID: PMC6405016.