Marine mammal Study Guide

📖 Core Concepts Marine mammals – mammals that rely on marine ecosystems for feeding and reproduction (e.g., cetaceans, pinnipeds, sirenians, sea otters, polar bears). Taxonomic groups – Cetartiodactyla (whales & even‑toed ungulates), Sirenia (sea cows), Carnivora (pinnipeds & relatives). Habitat dependence – Fully aquatic (cetaceans, sirenians) vs. semiaquatic (pinnipeds). Ecological roles – Keystone (sea otters), apex predator (polar bears, killer whales), nutrient cyclers (whale pump, whale falls). Major threats – Historical over‑exploitation, by‑catch, vessel strikes, habitat loss, noise, pollution, climate change. Conservation framework – Marine Mammal Protection Act (US), IWC moratorium, CMS, polar‑bear agreement, UN‑Law of the Sea. 📌 Must Remember ≈ 23 % of marine‑mammal species are threatened with extinction. Peak species richness occurs near ±40° latitude, matching high primary productivity. Diving adaptations: large O₂ stores (blood, myoglobin), bradycardia, peripheral vasoconstriction. Echolocation: clicks produced by phonic lips, focused by the melon. Baleen feeding – lunge‑feeding (mouth volume > body) vs. gulp‑feeding (continuous filtering). Whale pump – whales bring deep‑water nitrogen/iron to the surface via defecation, boosting phytoplankton. Key human‑impact numbers: North Atlantic right whale most affected by vessel strikes; sea otters nearly extinct before protection. 🔄 Key Processes Diving response Breath‑hold → bradycardia (↓ heart rate) → vasoconstriction (peripheral vessels) → O₂ utilization by heart & brain → anaerobic glycolysis from glycogen when O₂ depleted. Echolocation sequence (toothed whales) Generate high‑frequency click → focus with melon → emit into water → echo returns → processed by auditory cortex to locate/prey. Lunge‑feeding (large rorquals) Accelerate → open mouth → engulf water + prey → close mouth → force water out through baleen → retain prey. Whale fall succession Scavenger consumption → bone enrichment → sulfophilic bacterial colonization → chemoautotrophic community. 🔍 Key Comparisons Cetaceans vs. Sirenians – Fully aquatic, deep dives vs. shallow coastal, herbivorous. Baleen whales vs. Odontocetes – Filter‑feeding plates vs. teeth & echolocation. Pinnipeds vs. Sea otters – Semiaquatic, land‑dependent breeding vs. fully aquatic, use tools. By‑catch vs. Vessel strike – Entanglement leads to drowning/starvation; collisions cause blunt trauma and immediate death. ⚠️ Common Misunderstandings All marine mammals have blubber. → Only cetaceans and some pinnipeds rely on blubber; sea otters use dense fur. Echolocation is used by all whales. → Only toothed whales (odontocetes) echolocate; baleen whales do not. Polar bears are “fish” → They are terrestrial mammals that hunt seals from ice; they only opportunistically fish. 🧠 Mental Models / Intuition “Air‑bag vs. balloon” – Dive‑adapted mammals are like sealed air‑bags (large O₂ stores, low metabolic rate) while shallow‑water species act like balloons (smaller stores, less bradycardia). “Keystone → cascade” – Remove sea otters → urchin explosion → kelp forest collapse → loss of habitat for many fish. “Nutrient elevator” – Whales act as elevators moving deep nutrients to the surface; think of a freight elevator delivering supplies to the top floor. 🚩 Exceptions & Edge Cases Deep‑water cetaceans often have reduced bone density for neutral buoyancy, opposite to dense‑bone sirenians. Polar bears can switch to fish (Arctic charr, sculpin) when seal hunting is limited. Some pinnipeds (e.g., walruses) feed primarily on benthic invertebrates, not fish. 📍 When to Use Which Identify feeding strategy → Look at mouth morphology: teeth → predatory/odontocete; baleen → filter‑feeding. Assess threat level → If species is large, slow‑reproducing (e.g., right whales), prioritize vessel‑strike mitigation; if small, prioritize by‑catch gear modifications. Choose conservation tool → International treaty (IWC) for whaling bans; MMPA or speed‑restriction zones for vessel strikes; gear‑exclusion devices for by‑catch. 👀 Patterns to Recognize Depth‑range + prey type → Deep‑diving cetaceans → squid/large fish; shallow‑water sirenians → seagrass. Seasonal migration cue → Ice cover & temperature → polar bears, baleen whales. Noise‑impact → Species relying on echolocation (dolphins, porpoises) are especially sensitive to low‑frequency ship noise. 🗂️ Exam Traps Distractor: “All marine mammals have blubber” – confuse sea otters (fur) with cetaceans. Near‑miss: “Echolocation is used to locate prey and filter water” – only toothed whales use clicks for prey detection, not baleen whales. Trick: “Marine mammals are not affected by climate change” – ignore the strong link between sea‑ice loss and polar‑bear/seal populations. Pitfall: “By‑catch only harms small cetaceans” – large cetaceans can also suffer entanglement and reduced feeding, leading to starvation. --- If any heading lacked sufficient source detail, it would read “- Not enough information in source outline.”